Macbeth himself is more foul than fair in becoming Thane of Cawdor and later king, as the witches predicted. Although he rises in rank, he does so by giving in to ambition and committing regicide. Lady Macbeth tries to seem fair when King Duncan is their guest; beneath the welcoming surface, she is acting foul in plotting his murder. In fact, according to Duncan's son Donalbain, all people may be foul even though they seem fair: the "daggers" that men hide in their smiles show that they cannot be trusted.

One foul place that seems fair to Duncan is Glamis Castle. Upon his arrival there, he views it as "a pleasant seat." However, he will soon die there. A second place that is both fair and foul is the battlefield, as Macbeth describes the outcome of the war: "So fair and foul a day I have not seen." His victory makes the day fair, but the heavy loss of life makes it foul. In the final scenes, Dunsinane Castle seems fair, because it is apparently completely secured; however, for Macbeth it proves foul as the site of his downfall.

Regarding things, one object that seems foul but is not is the dagger that Macbeth sees before him. He believes it is the murder weapon, but he is just imagining the "fatal vision." The human face can also be foul when it seems fair; Macbeth says that a face is false when it hides what is in "the false heart" inside the person. According to Lady Macbeth, a flower may also seem fair but hide something foul. When Macbeth greets King Duncan, Lady Macbeth says that he should seem “like the innocent flower / But be the serpent” that lurks unseen beneath it.

I have suggested that the three witches in Macbeth are expressing their own perspective because they themselves are about as foul as three women can get. To them whatever is fair is foul because it makes them feel envious and spiteful, whereas whatever is foul seems fair because it is like themselves. This expresses an important and readily observable truth about human nature. People judge others by themselves. Wicked people are always attracted to wicked people, and they tend to despise people who are not as greedy, dishonest, mean-spirited, and treacherous as themselves. Birds of a feather flock together. You can see it all around you. You can see it in your school if you observe. It is a misfortune for a decent, intelligent, honorable boy or girl to fall in with a bad crowd, because they will do their best to corrupt him or her.

In Shakespeare’s King Lear, the Duke of Albany has a quarrel with his wife Goneril and tells her:

Wisdom and goodness to the vile seem vile.

Filths savor but themselves. (4.2)

In Shakespeare’s The Tempest, Caliban, who is a foul, vicious character, meets up with newly arrived Stephano and Trinculo, who are a couple of drunken good-for-nothings, and thinks they are semi-divine creatures. He asks Stephano, “How does thy Honor? Let me lick thy shoe." The whole of Act 2, Scene 2, illustrates how fair is foul and foul is fair and how birds of a feather instinctively flock together.

I don’t believe the witches in Macbeth are predicting what is going to happen in the play but are expressing the feelings of three loathsome creatures about the world they inhabit. Whatever is bad is good and whatever is good is bad—from their warped point of view. They are consumed with hatred because of their ugliness and wretched condition. They are always together.

In our contemporary world a beautiful girl or a handsome boy will often find that some people seem to take an instant dislike to them for no apparent reason. There is a reason, all right.

The theme of "fair is foul and foul is fair" runs throughout Shakespeare's play, Macbeth.

Note the appearance of the three witches: first when they meet Macbeth on the heath after the battle with Norway has been won, and later when they conjure apparitions and prophecies for Macbeth. In Act One, scene three, Macbeth introduces the theme:

MACBETH:

So foul and fair a day I have not seen. (39)

Next, the witches give Banquo and Macbeth predictions of what the future holds, but it is Macbeth (with his vaulting ambition—our tragic hero's flaw) who takes these words to heart and ultimately decides to murder his King, Duncan.

The theme applies here because the witches' predictions sound wonderful ("fair" or good), but they are evil—for their intent is to trip up Macbeth to the point that he will sacrifice his eternal soul in not only Duncan's death (for it was a mortal sin to kill a king), but for all the other horrible things he does to keep his place on Scotland's throne (and these things are "foul" or bad).

FIRST WITCH:

All hail, Macbeth! hail to thee, Thane of Glamis!

SECOND WITCH:

All hail, Macbeth! hail to thee, Thane of

Cawdor!

THIRD WITCH:

All hail, Macbeth, that shalt be King hereafter! (50-53)

Once the prediction for Cawdor comes true, Macbeth believes that the last one—that he will be king—is guaranteed. Banquo warns Macbeth of the "fair is foul" theme:

But ’tis strange;

And oftentimes, to win us to our harm,

The instruments of darkness tell us truths,

Win us with honest trifles, to betray's

In deepest consequence— (132-136)

Banquo notes that evil "truths" ("fair") can lead to destruction ("foul"). Macbeth ignores the advice. The witches' second set of predictions simply solidify Macbeth's belief that he cannot be vanquished, even though the also decides to kill Macduff and his family—just to be sure.

"Fair is foul" is found with Banquo's death as Macbeth tries to explain it away, noting that it is dangerous to go out at night after dark. In truth, Macbeth ordered Banquo's murder, knowing that Banquo was so ethical that he would never be able to keep his knowledge of the witches' predictions (which would point to Macbeth's part in Duncan's death) a secret. Banquo is a good man ("fair"); he is murdered because of Macbeth's evil intent ("foul").

Fleance's death is an example of "fair is foul" because he (Banquo's son) is completely innocent ("fair"), and he flees for his life—while his father is being murdered. Macbeth tries to blame Fleance for his father's murder—this is "foul."

In Act Three, scene four, lines 5-7, Lennox, a lord in Macbeth's court, speaks to another lord with dripping sarcasm—explaining how Macbeth gives socially acceptable excuses that cover up the truth of what is really going on (and his lies seem "fair"), but the truth is that these murders are visited only upon those closest to Macbeth—or in his way ("foul").

Till the end, Macbeth believes the witches; facing Macduff, he tells his enemy he cannot hurt Macbeth—he is protected by the prophecies:

Thou losest labor. (V.viii.11)

I bear a charmed life, which must not yield

To one of woman born. (15-16)

Ultimately, Macbeth realizes what has happened. While the witches promised him a multitude of desirable things ("fair"), Macbeth realizes the witches' betrayal ("foul"):

MACBETH:

And be these juggling fiends no more believed,

That palter with us in a double sense,

That keep the word of promise to our ear,

And break it to our hope. (23-26) 

When the Battle's Lost and Won

Macbeth is a play based on contradictions and equivocations. There is a contradiction on almost every page. I'm as sure as I can be that Shakespeare planned it that way. Indeed, the witches themselves rely on double meanings and contradictions all the time:

Lesser than Macbeth, and greater.

Not so happy, yet much happier.

Thou shalt get kings, though thou be none.

So all hail, Macbeth and Banquo!

Banquo and Macbeth, all hail!

Want more? Lady Macbeth asks to be unsexed and Macbeth later says to her:

Bring forth men-children only,

For thy undaunted mettle should compose

Nothing but males.

And she refers to him as a woman:

O, these flaws and starts,

Impostors to true fear, would well become

A woman's story at a winter's fire,

Authorized by her grandam.

More? The porter's speech before answering the knock the door is all contradictions:

Here's a farmer that hanged himself on th’ expectation of plenty...here's an equivocator that could swear in both the scales against either scale, who committed treason enough for God's sake yet could not equivocate to heaven...here's an English tailor come hither, for stealing out of a French hose...But this place is too cold for hell.

More? In Act 4, Scene 3, the entire first part of the conversation between Malcolm and Macduff is equivocation and contradiction. Malcolm is telling Macduff things about himself that are comletely opposite of the truth.

I could give you much more, but just know that the play, Macbeth, is based upon the idea that the world has been turned upside down: good is seen as evil, evil as good, men act like women, women act like men, truth is taken for lies and lies for truth, killing is good and then killing is bad, and so on and so on. "Fair is foul, and foul is fair," for sure and everywhere.

OK, here's one more in parting:

Angels are bright still, though the brightest fell.

Though all things foul would wear the brows of grace,

Yet grace must still look so.

Just open to any page and there they are, like bones that support the body.

Seeing that this is a theme of the play, it can be found in several moments.  The very idea that Lady MacBeth would conspire with MacBeth to slay the king is representative of this line.  The underlying premise of the line is that what is considered to be immoral or unjust has been created or conceived to be action to be taken.  The moral order that used to uphold reality has been suspended and in its place, the inverse of this structure can become the new structure.  Moments where what could be deemed as one thing, but actually represent another can be seen.  The presence of the witches, themselves, might be such an example.  On one hand, the three witches could be seen as something evil or unholy, definitely to be rejected.  However, their presence being embraced by Macbeth would be another instance of "fair is foul" and the idea that things are not what they seem to be.  Extending this would be Lady Macbeth's acknowledgement of wrong and her complicity.  On one hand at the start of the play, she is the embodiment of the animating spirit behind immoral actions.  Yet, through the course of the play, she becomes increasingly timid, being wrapped and subsumed the force of her own culpability.  Her death at the end of the play, triggering  Macbeth's final soliloquy reflects the idea of things might be different that what they seem to be.

I will not even ask why you are explaining this to a first grader, since I had my 8th graders make picture books for little kids last year when we performed Macbeth.  They weren't allowed to see the play, because of the blood.  However, I would explain it as"What's good might be bad, and what's bad might be good, so lets float through the fog and gross air."

Sometimes things are not really what they look like. In fact, something that looks like it is good to eat may actually make you sick.  We must be careful to know what something really is before we eat it, or play with it, or even touch it.

For a first grader: "Good is bad. Bad is good. Let's fly through the dirty air."

Shakespeare's Macbeth opens in "a desert place" with three witches. The witches briefly converse with each other, mentioning that they will meet again when they see Macbeth and closing their meeting (and the scene) with this joint statement:

Fair is foul, and foul is fair:
Hover through the fog and filthy air.

There is much that can be discussed about this line. If we want to focus on fate and prophecy, we should first discuss the witches themselves.

The witches clearly have some amount of knowledge. They know who Macbeth is (current thane of Glamis) and know where to meet him at the heath near forest. However, it can be debated to what extent the witches know the future. Do they truly predict the future? Are they simply able to see the future and just telling what they have observed? Are they actively changing the course events through their interactions with Macbeth?

The title character does not appear until scene three, after the audience has already seen the witches a second time. Macbeth's first utterance is:

So foul and fair a day I have not seen.

It is significant that his first line repeats the phrase that the witches said. The day is foul, meaning the weather is bad. There is thunder whenever the witches enter, so we might already start to question the idea of fate. Do the Witches cause the thunder? Are they responsible for the foul day, or do they just like to appear during a storm? The day is fair for Macbeth because he won a great victory; he personally succeeded in battle, but also his side won overall. However, looking back we would name this as the day his troubles began, so perhaps it is not so fair (fair is foul).

At this point, the audience knows that Duncan has named Macbeth the new thane of Cawdor, but Macbeth does not. He hears the witches say this as a "prophecy," but we should wonder if it is truly a prediction of theirs, or if they simply have this knowledge like we the audience do. When Ross tells Macbeth the news, to him it seems as if it is a prediction coming true. He is now more inclined to believe the other things the witches say. The question now is whether those things will automatically come true, or if they are only set in motion by Macbeth's choices the rest of the play. He considers:

This supernatural soliciting
Cannot be ill, cannot be good

His musings play upon the idea of "fair is foul and foul is fair." Is this ill or good? Can it be neither? Can it be both? The prophecies are fair and bring good news to Macbeth (the idea of being King). And yet it is foul, because being King is Macbeth's downfall. We learn later in the play that he is not a good king, and Scotland suffers under his reign. It is foul indeed.

Macbeth: Your children shall be kings.

Banquo: You shall be king.

Repetition is often used to not only emphasize an idea, but set up a comparison. Later, the witches show that Banquo's line will rule Scotland, but Banquo does not act upon this prediction. Macbeth, conversely, does. He murders Duncan so he can be king. We wonder if this is fate, always meant to happen, or if it is a self-fulfilling prophecy: would Macbeth have murdered Duncan had he not come across the witches?

The words "foul" and "fair" are repeated throughout the play:

Away, and mock the time with fairest show

False face must hide what the false heart doth know. (act 1, scene 7)

They appear again later in the play:

Thou hast it now: King, Cawdor, Glamis, all,

As the weird women promised, and I fear

Thou play'dst most foully for't. (act 3, scene 1)

In Shakespeare's The Tragedy of Macbeth, the audience hears the three witches chant these words in unison at the end of Act I, scene I. They have made a plan to meet Macbeth, and by saying "Fair is foul, and foul is fair," they are telling the audience that not everything is as it seems.

One example of something that seems "fair" but turns out to be "foul" is Macbeth himself, a war hero who turns murderer. One example of something that looks "foul" but turns out to be "fair" is the battle that took place as a result of the Thane's rebellion against the king; though the battle is bloody, it gives Macbeth the opportunity to impress Duncan, which makes for a fair situation for Macbeth.

This warning puts the audience members on the lookout for situations that might seem suspicious. This warning also contributes to the mysterious and supernatural nature of the witches, who do not communicate in clear language like the human characters in the play.

The three Weird Sisters seem to mean that people who look "fair" are often deceiving, and they may be referring specifically to Lady Macbeth. As far as "foul is fair" is concerned, they may be referring to themselves, because they are horrible-looking but are offering honest advice. Duncan is speaking of the traitorous Thane of Cawdor when he says that there is no way of judging a person's character from his appearance. This is at a time when he is about to be murdered by Macbeth and Lady Macbeth, who are welcoming him with the utmost cordiality. Lady Macbeth is especially good at hiding her true character and her secret thoughts. She is flattering the King outrageously while secretly planning to murder him that very night.

Is it really true that there is no way of judging people from their appearance? I don't think so, even though wicked people will always try to hide their true natures. We should always be a little suspicious when people, especially strangers, are too friendly. Perhaps Duncan should have been a little more suspicious of his host and hostess, especially after being double-crossed by the Thane of Cawdor. Duncan should have asked himself why Lady Macbeth was acting so exceedingly joyful to see him and to have him as her overnight guest. The audience, of course, knows that her behavior is completely phoney and can appreciate how good she is at dissimulation. But Duncan ought to have been a little smarter. After all, he has lived a long time, and he is the King.

The three witches are thoroughly evil. As such, they hate what is good and like what is wicked. In saying "Fair is foul and foul is fair" they are expressing their own values. Later one will brag about killiing swine and another will brag about causing great hardships for the sailor-husband of the woman who refused to give her chestnuts. They admire what is foul and despise whatever is fair. Naturally they would hate young and attractive women, since they themselves are so horribly ugly. This would seem to be expressing Shakespeare's own assessment of evil people. It can be observed in present-day reality that bad people like bad people and tend to despise and mock good people. Birds of a feather flock together. Their wickedness influences Macbeth, who gradually becomes like them in hating what is good and delighting in his own worst qualities. The best expression of this idea can be found inKing Lear, Act 4, Scene 2, where the Duke of Albany says to his hateful, thoroughly wicked wife Goneril:

Wisdom and goodness to the vile seem vile:

Filths savour but themselves.

This is a truth and a warning worth remembering.

By saying that "fair is foul" and "foul is fair" the witches are foreshadowing some of the evil that is to come in the play. Shakespeare is setting the tone for the play, which is almost unrelentingly dark and foreboding. They are also establishing the fact that in the play, sometimes things are not as they seem.

Macbeth becomes the king of Scotland, but he is a usurper, occupying a throne that does not belong to them. The song, which concludes a very short scene that began with thunder crashing ominously and is full of references to foulness and evil, is not just an idle tune. The witches are predicting the future course of events in the play. Indeed, many argue that they are actually responsible for these events. 

"Fair is foul and foul is fair," first uttered by the witches in Act 1, Scene 1, is a paradox that sets the stage for the entire play.  At its most basic,  it means that "good is bad and bad is good."  In the context of the play itself, it means that things that are good are also bad and vice-versa.  For example: Macbeth's murder of King Duncan is good for Macbeth, as it leads him to become the kind of Scotland, but bad for King Duncan.  To continue to explore this particular example: Macbeth's reign is initially good for him and Lady Macbeth, but bad for the country.  In Act 4, Scene 3, Macduff complains of Macbeth's rule, stating that "Each new morn / New widows howl, new orphans cry, new sorrows / Strike heaven in the face," thus revealing that conditions in Scotland grow increasingly worse under Macbeth's rule (5-7).  Even this very scene is representative of another way in which the "fair is foul" motif is present.  In this scene, Macduff is in England, attempting to persuade Malcolm, the rightful king, to return to Scotland to fight against Macbeth.  Some believe that Macduff has "fled" to England because he is a coward (foul), when in reality he has left because he is willing to risk his own safety to fight against Macbeth (fair).  Further, Malcolm is initially suspicious that Macduff is working for Macbeth, and has come to England to trick Malcolm into returning so that Macbeth can kill him (foul).  Because of this, he pretends to be worse than Macbeth (foul) but in reality he is loyal to Scotland (fair) just as Macduff truly is (fair).  

Unsurprisingly, Shakespeare does a masterful job of weaving this motif upon itself throughout Macbeth.  Macbeth's act of regicide is initially fair for him and his wife, but becomes foul as the guilt of the act grows, combining with Macbeth's own paranoia and eventually leading to his downfall.  This is just one of many ways in which it appears, but it is one of the best examples to demonstrate the intricacy of the "fair is foul" concept.

It could be construed as whatever is "fair" could also be "foul" and whatever may be "foul" could also be "fair." Think of this in terms of an "eye for an eye." This statement could be seen as foreshadowing the events to come within the play.

In act 1, scene 1, the Three Witches comment on how they will meet again upon the heath, where they shall introduce themselves to Macbeth. Before they exit the scene, the witches recite, "Fair is foul, and foul is fair: Hover through the fog and filthy air" (Shakespeare, 1.1.12–13). The phrase "Fair is foul, and foul is fair" is a paradox and motif that runs throughout the entire play and essentially means that appearances are deceiving. The phrase is considered a paradox because it is a statement that seems to contradict itself but contains a hidden truth. According to the phrase, whatever seems good is really bad, while the things that appear to be bad are actually good. There are numerous examples of appearances being deceiving found throughout the play, beginning with Macbeth's seemingly optimistic prophecy about becoming King of Scotland. While the prophecy seems positive, it influences Macbeth's ambitious nature, and he develops into a bloodthirsty tyrant. King Duncan initially believes that Macbeth's castle is pleasant and welcoming, while it is actually ominous and threatening. Lady Macbeth and Macbeth conceal their true emotions by acting like gracious hosts while they plot Duncan's murder. The second set of prophecies also seems positive but makes Macbeth overconfident and leads to his demise. Overall, the phrase "Fair is foul, and foul is fair" is a motif that runs throughout the play and means that appearances can be deceiving.

This line comes from Act I, Scene I, and it is chanted by the three witches as they await the end of the battle. At first glance, this line is a paradox since it is not possible for something to be "fair" (nice) and "foul" (horrible) at the same time. However, this paradox is central to understanding what the witches truly mean: by using this line, they are warning the reader that everything is not quite as it seems in this play. In other words, appearances can be deceptive, and the reader must not take the play's events and characters at face value.

As the play progresses, the relevance of this line becomes more apparent and is proven true through the character of Macbeth. On the surface, Macbeth is the ideal thane: he is loyal to the king and fights bravely in battle. But Macbeth is quickly and easily seduced by the prophecy that he will become king, and he soon begins planning Duncan's murder. Therefore, Macbeth seems to be "fair," but he is really quite the opposite.

We encounter this quote twice early in the play. The witches chant "what's fair is foul, what's foul is fair / hover through the fog and filthy air" when they leave to meet Macbeth after the battle. Shortly before meeting the witches in Act I, Scene 3, Macbeth says to Banquo that he has never seen "so foul and fair a day." He means, essentially, that they have won a great battle, but at a horrible cost, with blood and death all around them. The witches' meaning is less clear, but their rhyme (reinforced by Macbeth's observation) establishes a crucial theme for the play. Appearances will be deceiving, and what appears to be good will in reality be evil. We see this in several instances. Lady Macbeth, for example, plays the dutiful hostess to Duncan, who she and her husband are plotting to kill. Macbeth's rise to the throne is made possible by a trail of murder. The witches' prophecies, while apparently very fortuitous to Macbeth, in fact lead him largely unsuspecting down a path to his own destruction. So the idea that what is "fair" is "foul" runs throughout the play.

In Macbeth, the witches' equivocal language is a duality, a riddle, a kind of spell, a critique of the society, and an example of foreshadowing and verbal irony. Really, the statement is a way of showing that the natural order has been inverted, that the bottom of the Great Chain of Being (witches and murderers) will replace the top, the King, God's holy vessel.

Literally, as eNotes's "Text in Translation" says, it is "Beautiful is disgustingly filthy, and disgustingly filthy is beautiful." Certainly, this is a commentary on the witches themselves, as they are old hags at the bottom of the socio-economic ladder. By Act III, they will become the King's most trusted advisors. So, it is a foreshadowing and an irony.

Other interpretations:

• Good is evil; evil is good. The good King Duncan will be replaced by the evil King Macbeth.
• Loyalty is betrayal; betrayal is loyalty. The act of murder will subvert the code of the thanes.
• God is the devil; the devil is god. As the King was considered God's Holy Vessel, his murder will open the door for the devil's chaos.
• Natural becomes unnatural; the unnatural becomes natural. After Duncan's murder, there are earthquakes, horses eating each other, bloody babies, moving forests, and all kinds of sinister and horrifying acts that subvert the natural order.

In Shakespeare's Macbeth, the line "Fair is foul, and foul is fair," is first said by the witches in Act 1.1, and then echoed by Macbeth in Act 1.3.

Literally, the line means that what appears to be fair, is actually foul, and vice-versa when Macbeth echoes it.

Figuratively, though, the line accomplishes much more than the revealing of the literal meaning.  It introduces and contributes to themes revealed in the play, and also immediately reveals a connection between Macbeth and the witches.

At the time Macbeth utters the line, he is literally referring to the weather, as are the witches when they use it.  Macbeth at this point in the play is a war hero and loyal protector of his king.   The witches are grotesque and crass.  Yet, the separate speakers of the line are connected when Macbeth uses it.  This foreshadows their relationship.

Throughout the drama, what appears to be fair is often actually foul.   Duncan says Cawdor appeared to be loyal, just as Macbeth appears to be loyal.  Lady Macbeth warmly greets Duncan when he arrives at her castle, though she is planning on assassinating him.  Macbeth appears to Banquo as his ally, but he orders his death.  Macbeth is king, and appears to be telling the truth when he informs the murderers that it was Banquo, not Macbeth, who wronged them, but he is lying. 

Even when fair is fair, it is suspected of being foul, as when Macduff is suspected of treachery by Malcolm.

Opposites also appear in the play, echoing this quote.  The witches appear to be women, but have beards.  Macbeth, the warrior, feels pity and guilt before and immediately after he kills Duncan, emotions more often associated with females.  Lady Macbeth, on the other hand, asks to be unsexed, turned from female to male.

This single line introduces and contributes to much of what is revealed in the play.

This quote comes from the end of the first scene of the play.  It is spoken by the witches.  They are, in this case, giving a bit of a prophecy about how the play will go.

What they are saying is that things that seems fair (good) are really foul (bad).  And things that seem foul are really fair.  What this prophecy is supposed to do is to show that morals are going to be lost in this play.  Everything is going to be up for grabs and the events of the play will really be confused and mostly evil.

This is from Act 1, sc. 1 and the line is spoken by the Weird Sisters (witches).  They say it as a chant and the words set the scene for the play.  The words indicate that appearances will be deceiving - what one sees as "fair" may actually be "foul" and what one sees as "foul" may actually be "fair".  The witches tell us also, in this scene, that they are going to meet with Macbeth which lets us know that Macbeth is going to be the one they mess with.  The words also indicate one of the major themes of the play which is that one should not trust appearances.  There are many references to this idea throughout the play.  Even Duncan makes reference to it in Act 1, sc. 4, when he says, "There's no art / To find the mind's construction on the face." In Act 1, sc. 5, Lady Macbeth tells her husband to put on a false face because his face tends to show his emotions - "To beguile the time, / Look like the time;...look like the innocent flower, / But be the serpent under't."  Macbeth's final words in the first act are, "False face must hide what the false heart doth know."  Before he and Malcolm flee Scotland, Donalbain says, "There's daggers in men's smiles;". Of course one of the major examples of this theme is in the visions that the weird sisters show Macbeth in Act 4, sc. 1.  Those visions give Macbeth a false sense of security which lead to his death at Macduff's hands.

Okay, you've got a ton of answers here, but what I believe is the intention behind these words, (the reason the witches say them), is because they are making an incantation. They are not just making an observation about the nature of things as they see them. In theatre, every character is engaged in action. The witches are powerful characters and Shakespeare has them at the beginning of the play for a very specific purpose, which is to set up the atmosphere for the whole of what's to come. The lines we are addressing are deliberately spoken....a state of affairs willed into being....by the witches. We are witnessing the creation by the witches of a reversal in the ordinary nature of things. Here we witness an incantation creating an environment for the whole play that follows, which turns right into wrong, good into bad, and all things bright into gloom. This incantation helps to set the tone and direction for the play.

I agree with most of the statements regarding this line, but there is one very important element that has been left out. Shakespeare was a dramatist first and foremost and every word he wrote connects to action. The witches are not simply observing something with that line. They are actively doing something, as must always be the case in a successful theatrical text. They are actively affirming that "fair is foul, and foul is fair." When the witch speaks this, she is affirming that this is the case, in the way we speak affirmations to produce what we want to be so. It is neither a rumination nor an observation. It is a statement of 'making.' They are creating a condition by affirming it.

This statement by the apparitions reminds me of a statement in the Bible where it states, not a direct quote, good becomes bad and bad becomes good. As was already mentioned, something may be the morally right thing to do and you do it or you decide to do contrary to what you know is right. In many cases, it can be because of the current standards around you or because of a degredation of ones own standards of morality. We saw this with MacBeth as he gradually went away from what reasonable, discerning people would, hopefully, know to be wrong; excessive pride, greed, untamed power, etc.

The binary between fair and foul to normal people with socially acceptable code of conducts, makes the Witches' statement an enigma and a paradox. To the normal human world what is foul cannot be fair. But what Shakerspeare suggests is that the Witches's invert and subvert the morality and ethics of the human world. There is no foul/fair binary in the witches's world.

metaphorically, the witches's statement is also a commentary on appearence and reality. What might appear to be fair may be foul in reality. Thus Macbeth, the 'valour's minion' and 'Bellona's bridegroom' commits a most ignoble act of murdering Duncan, who sees Macbeth as an embodiment of good and trustwothiness. Similar instances of the dichotomy between appearence and reality abound in the play.

There is no reason to think that the witches are telling the truth. There is no reason to think that they know the truth. There is no reason to attach much importance to their statement that "Fair is foul and foul is fair." The truth is probably that fair is fair, but they find it foul because they hate everything that is fair and good. They would find a beautiful woman ugly because she puts them to shame and probably find an ugly woman beautiful because she would resemble themselves. Everything that is fair is foul--to them, and everything that is foul is fair--to them. They are horrible creatures in their physical appearances, and they have equally horrible minds. They delight in doing wicked things. Bad is good to them, and good to them is bad. This is not a description of reality but an expression of their opinion. In King Lear the Duke of Albany tells his wicked wife Goneril, "Wisdom and goodness to the vile seem vile / Filths savour but themselves."

It occurs to me that the witches are not saying two different things but are saying the same thing in two different ways and that they can only be referring to Lady Macbeth because there is no other character in the play who can be described as "fair." It would not be appropriate to describe Macbeth or any other male as "fair." Lady Macbeth, however, must be thought of as exceptionally attractive if she can have such a strong hold on her husband. The witches, being female themselves, might be especially interested in Lady Macbeth because they are ugly and possibly jealous. The word "fair" should make us think of a beautiful woman. The witches are not talking about picturesque landscapes or using the word as a metaphor for a good outcome in a battle. Lady Macbeth may be called fair but foul because she is fair on the outside but foul on the inside. She may also be called foul but fair for the same reason: she is foul on the inside but presents a fair appearance. There are many fanciful ways of interpreting what the witches say, but I can see only one literal meaning to their words, i.e., that Lady Macbeth is fair and foul and foul and fair. She will be the one who leads Macbeth to his doom. Without her goading and sexual extortion, Macbeth would not have murdered King Duncan. She uses her beauty and sex appeal flagrantly and ruthlessly in order to manipulate her doting husband.

The scene, in its original setting, a stage with minimal scenery,  seeks to separate the "real" world from the world of the witches, and part of that effort is to establish the barren, wind-blown Scottish heath, the home of the witches.  When they say "Fair is foul and foul is fair," they are contrasting their ideal climate with the climate that the audience, and the other characters, would consider ideal. Paraphrasing:  "What is foul to you is ideal, is 'fair' for us; we like 'foul' weather."  "Our ideal world, where fillet of fenny snake and eye of newt and tongue of bat can be combined to conjure up visions and predictions of the future, may be ugly to you but it's ideal for us and our leader, Hecate."  The phrase also points to the coming imbalance of natural order, the chaos of lost kingships (or thaneships).  It shows that this world is out of order, because of the breakdown of the Great Chain of Being.

I wish I could answer that as straightforwardly as you ask it!

What the line points to is the play's concern with the discrepancy between appearance and reality: that is, the difference between how someone seems and how someone is. It is a central concern of Shakespeare's, and obviously one that fits well with the medium of theatre, which relies on actors seeming to be something that they most definitely aren't.

Macbeth, when he - almost - quotes the line on his first entrance, turns it into a remark which juxtaposes his victory with the weather:

So foul and fair a day I have not seen.

The weather is "foul" - bad - but the day (meaning "the outcome of the battle": hence "the day is yours") is "fair" - good, because they have won. The day is foul and fair at once.

That said, none of that is really any help to us with the witches' enigmatic line, which says simply that bad is good, and good bad. It's rather like when Macbeth says that "nothing is, but what is not" - a difficult, knotty idea that, in the world of this play, nothing is the only something. Foul is fair. Fair is foul. It's a world where nothing is what it seems. It's a world where you're never sure whether it's a real dagger or an apparition, a mirage, or the ghost of Banquo. It's a world where you can't trust anyone. Not even the witches.

This is one of the last lines in Act 1 Scene 1 when the witches are foreshadowing events to come in the play. With these words, they are predicting the evil that will cloud Macbeth's judgments and that those judgments will appear to Macbeth as fair and just. This line also could refer to the witches believing that things most men consider to be foul and ugly are just and beautiful to them because they embody evil. This gives the reader insight into what actions the witches are going to encourage from Macbeth.

On the most basic level, it means that things are reversed.

To expand on that a little bit, it means two related things in general. First, it means that things that are good will become bad and things that are bad will become good. Second, it means things that look pretty ("fair") will become ugly ("foul") and things that are ugly will become beautiful.

The witches are referring first to themselves. They look ugly, but the predictions they offer are beautiful to Macbeth.

They are then referring to the entire world of the play. If you look at Duncan's first lines, at the start of scene 2 in Act I, the normal humans are operating in a world where appearances honestly and accurately represent reality. Likewise, Macbeth is tagged as praiseworthy by the soldier's report—and he deserves it.

However, as soon as Macbeth meets the witches, everything changes. He hears great predictions, but they lead him to evil actions. He starts lying and deceiving, and no longer can anyone trust anyone else's face to reveal his or her character.

Greg

This statement is a paradox, an apparent contradiction that is actually true. What is means is that values have been reversed. What is good will be bad and what is bad will be good. Appearances will be deceiving. These lines, which appear at the very beginning of the play, contain a major theme of "Macbeth". The meaning is mirrored often in the play,but especially at the end.

"Fair is foul and foul is fair" is a theme that suggests how appearances differ from the reality beneath the surface.  A good example of this is how Lady Macbeth schools Macbeth to "look like the innocent flower/But be the serpent under't."

From the time we first meet her in Act I, scene v, Lady Macbeth is concerned about the goodness in Macbeth that she perceives as weakness.  She wants to alter his natural, honest behaviour to create a two-faced murderer, able to smile and shake Duncan's hand, while simultaneously plotting the King's murder.

When she first suggests the potential that Duncan be murdered in their home, she comments on how easily Macbeth's face gives his true feelings away:

Your face, my thane, is as a book, where men

May read strange matters.  To beguile the time,

Look like the time.

So, Lady Macbeth schools Macbeth in how to appear "fair" while remaining "foul" underneath.

She displays her own skill in this art at the banquet in Act III, scene iv.  Even when she doesn't know exactly what has spooked Macbeth, she strives desperately to put a "fair" face on what is certainly a "foul" moment.  She assures the lords assembled:

Sit, worthy friends.  My lord is often thus...

The fit is momentary.  Upon a thought

He will again be well.

And she condemns his inability to ignore the "foul" (Banquo's ghost) and put on a "fair" face as womanly behaviour:

This is the very painting of your fear.

...O, these flaws and starts,

Impostors to true fear, would well become

A woman's story at a winter's fire....

Why do you make such faces?  When all's done,

You look but on a stool.

Of course, by the end of the play, Lady Macbeth's ability to put a "fair" face on what is "foul" completely breaks down and she dies from her own mad imaginings.

.

Well done for identifying the key theme from what the witches say at the beginning of the play. "Fair is foul and foul is fair" is certainly a motto that can be applied to so much of this excellent tragedy. For me, what this soliloquy represents is the further moral degeneration and paranoia of Macbeth as a character. Note how just before Macbeth begins his soliloquy, he bids Banquo farewell by saying:

I wish your horses swift, and sure of foot;

And so I do commend you to their backs.

He then goes on to plot the death of both Banquo and his heir, Fleance. We have already seen how the theme of "fair is foul and foul is fair" has been enacted throughout the play up to this point, with Macbeth and Lady Macbeth outwardly pretending to be devoted subjects of King Duncan whilst secretly plotting his murder. This again then represents a continuation of this theme as Macbeth outwardly wishes Banquo a good ride but inwardly is plotting his destruction.

Macbeth of course justifies his murder of Banquo by saying that it is only Banquo that gives him fear because of his qualities, which are in many ways superior to Macbeth's:

Our fears in Banquo

Stick deep, and in his royalty of nature

Reigns that which would be fear'd: 'tis much he dares;

And, to that dauntless temper of his mind,

He hath a wisdom that doth guide his valour

To act in safety.

Thus, to secure his position and make sure that the witches' prophecy of Banquo's heirs becoming king does not become true, Macbeth decides to rid himself of Banquo and his descendants once and for all. Notice how this is a murder he plans by himself, and also one that he gets others to carry out - reflecting his increasing degeneracy as he removes himself from the act whilst orchestrating it at a distance.

By opening the play with these lines, Shakespeare establishes the mood and conveys the theme instantly.  What used to be good will begin to be bad, and what seems to be bad will become good.  This juxtaposition is one of the main themes of the play,  that ambition and greed can lead to destruction.

The witches serve as a sort of chorus for the play.  They establish Macbeth’s future as Thane of Cawdor and king.  Before the witches arrive and talk about things being foul and fair, Macbeth is a hero.  He has fought valiantly for the king and killed the traitors.  He is no coward, and seems to be interested only in success in battle.

Then the witches arrive.  They are about to turn Macbeth from fair to foul.  Things will no longer be black and white.  Everything will be mixed up.  The witches’ presence continually spurs Macbeth on to more and more violence.  They have told him he will be king.  They are a self-fulfilling prophecy.

Before meeting the witches, Macbeth comments:

So foul and fair a day I have not seen. (Act 1, Scene 3, enotes etext p. 12)

He reiterates the witches earlier comments, which he did not hear, and brings continuity to the concept and ties the concept to Macbeth.  Somehow, the day is both good and bad—as Macbeth is both good and bad at this point.

Banquo’s comments when he is suspicious of Macbeth also refer back to this line.

Thou hast it now: King, Cawdor, Glamis, all,

As the weird women promised, and I fear

Thou play'dst most foully for't: (Act 3, Scene 1, p. 40)

Banquo remembers what the weird sisters told them and what Macbeth said.  His choice of the word “foully” to describe Macbeth’s killing Duncan has double meaning:  Macbeth did not play fair to get the throne.

Malcolm also comments to Macduff that Macbeth is treacherous,

That which you are, my thoughts cannot transpose.

Angels are bright still, though the brightest fell.(25)

Though all things foul would wear the brows of grace,

Yet grace must still look so. (Act 4, Scene 3, p. 67)

These lines are hopeful.  Malcolm believes that if he and Macduff take back the kingdom, things can be good again.  He is right.  They are able to take out Macbth, and Malcolm regains the kingdom.  The evil is stamped out.  Ambition led to destruction, but what's bad is good again.

Part of how the line is proven is through the actions of Macbeth and Lady Macbeth.  The notion of an inverted set of values is seen when Lady Macbeth begins to plant the seeds of disloyalty and murder in her husband's mind.  This is when we begin to see the counsel of husband at the hands of wife not seek to broaden community or nurture, but actually sever and destroy.  The inversion of values and of morality is present in such a condition.  Throughout the moral depravity of both characters what was seen as horrific and something which could not be done becomes embraced and almost seen as common.  Into this moral abyss, Macbeth plunges himself without any frame of reference or detachment because "fair is foul, foul is fair."

This line is the most important line of the first scene.  It is the line that is said by all three witches.  It is comprised of monosyllabic words.  Obviously Shakespeare is calling attention to this paradox.  Its application to the witches is quite evident.  They are easily associated with evil forces, meeting in "thunder, lightning, or in rain."  They associate with cats and toads, and they "hover through the fog and filthy air."  So, of course, what seems fair to them may seem foul to others, and vice versa.  These witches, we later learn, enjoy creating misery and stirring up trouble.

Interestingly, though, Macbeth echoes the witches in the third scene with "so foul and fair a day I have not seen."  This line becomes more complex when uttered by Macbeth.  The weather, of course, has been stormy or "foul."  But Macbeth has won the battle against Norway.  His forture this day has been "fair."  Yet, his victory cost the lives of many men, so fair and foul are intermingled.  But it cannot be ignored that this phrase also links Macbeth to the witches who had earlier claimed that they were to meet Macbeth on the heath.  His words following those of the witches so closely seem to link him with their evil.

This connection becomes even more apparent when Macbeth hears his prophecy, which seems to be one of good fortune and fame.  Yet this fair prophecy is undermined by the foul thoughts that leap into Macbeth's mind when he hears that he may become king of Scotland.  He thinks the unthinkable:  assasinating Duncan.  Again fair and foul are intermingled.

With Lady Macbeth the phrase becomes even more layered.  She cautions Macbeth to "look like the innocent flower, but be the serpent underneath."  For her, fair disguises the foul.

These various applications of the expression can be seen throughout the play, but perhaps it most aptly applies to the topsy-turvy world that Macbeth creates when he disturbs the order and kills Duncan, becoming a tyrannical ruler.  In so doing, he turns fair men like Macduff into rebels who must commit treason to restore order.

In the play Macbeth by William Shakespeare, the quote "fair is foul, foul is fair" could be applied to the castle. It sounds like a lovely place - the sort of place where birds feel secure and contented enough to nest in its buttresses, where the weather might always be warm and the atmosphere sweet and welcoming. Welcoming indeed is Lady Macbeth, greeting her husband's guests like the perfect genteel wife and aristocratic hostess. But she is merely putting on a superficial show to gull the guests into a false sense of security and to hide the truth and the real motive. Underneath, everything in the castle is rotten and decaying and the scene for bloodthirsty events.

In Shakespeare's Macbeth, the witches first use the line you ask about in Act 1.1:

Fair is foul, and foul is fair.

Macbeth then echoes them in Act 1.3:

So foul and fair a day I have not seen.

First, Macbeth is identified with and connected to the witches by his echo.  but there is more to the similar quotes than just this.

The line establishes and contributes to the theme of illusion-reality in the play.  In Macbeth what seems to be fair is often foul, and even when the fair isn't foul, it may be suspected of being foul.

This is evident at numerous points in the play.  I'll mention a few.

Duncan tells Malcolm that there is no way to know what is on a man's mind by looking at a man's face, and that Cawdor, the traitor, was a man he had trusted absolutely.

Duncan trusts Macbeth, also, and Macbeth assassinates him.

Banquo is not in the process of rebelling against Macbeth, although he does suspect him of treachery.  Macbeth kills him because he suspects him.

Malcolm is not sure whether or not he can trust Macduff when Macduff comes to England to join Malcolm in a fight against Macbeth, so Malcolm puts him through a series of tests.  Macduff passes.

The witches equivocate and deceive Macbeth.  They tell him things which sound true, but are deceptively untrue.

The theme of illusion-reality is prevelant in the play, and is introduced and contributed to by the idea of the fair and the foul. 

The line "Fair is foul, and foul is fair" refers to the tension between appearance and reality. What this means is that things are not always what they seem. Appearance can be rather deceiving, as can be seen in this play.

Our tragic hero Macbeth appears to be a valiant and loyal soldier, who is there to protect and respect his king. At the beginning of the play, everyone admires him, and we can easily notice how respectable and liked he is. He is even promoted by the king himself for his bravery and loyalty. However, once we delve into Macbeth's thoughts, we see that he plans to murder Duncan for the sake of gratifying his unrestrained ambition to become the king. And, not only does he murder the king, but he also makes it clear that anyone else who stands in his way will be eliminated too.

Macbeth embraces evil, and his real character is soon known to everyone in the play.

Lady Macbeth and Banquo both die because of the transformation in Macbeth.  Both were fair, and become foul—either to themselves or to Macbeth.

The witches tell us that what is good is bad and what is bad is good.  In the case of Lady Macbeth, this is definitely true.  She thinks that Macbeth being king is a great idea, and even encourages him to kill Duncan so that he can be.  Then, he ends up killing several more people and she begins to wonder if she has created a monster.

Nought's had, all's spent,

Where our desire is got without content.

’Tis safer to be that which we destroy

Than by destruction dwell in doubtful joy. (Act 3, Scene 2, p. 45)

Lady Macbeth thinks that he should just sit back and enjoy what he has, but Macbeth is not secure.  He tells her that they have not gotten rid of the threat, and she begins to worry.  By Act 5, she is full of regret for what she has done.  She ends up killing herself because of the consequences of fair being foul.

The Thane of Fife had a wife; where is she

now? What, will these hands ne'er be clean? No more o’

that, my lord, no more o’ that. You mar all with this(40)

starting. (Act 5, Scene 1, p. 77)

The guilt of what he has done, and her part in it, destroys her.

Banquo was Macbeth’s trusted friend.  He was there when the prophecy was given.  Yet because he was named in the prophecy, and the witches said his sons would be king, Macbeth suspects him.  He tries to warn Macbeth not to listen to the witches, but Macbeth is too far gone.

The instruments of darkness tell us truths,

Win us with honest trifles, to betray's(135)

In deepest consequence—

Cousins, a word, I pray you. (Act 1, Scene 3, p. 15)

In the end, Macbeth decides that Banquo, once fair, is now foul.  He is nothing but a threat to be eliminated at all costs.

To be thus is nothing,

But to be safely thus. Our fears in Banquo

Stick deep, and in his royalty of nature

Reigns that which would be fear'd. ’ (Act 3, Scene  1, p. 42)

Before long, Macbeth kills Banquo.  He proves again that fair is foul, since the two were friends but he is willing to kill his friend to secure his ambitions.

In Shakespeare's Macbeth, one of the witches' first utterances in the play sets the tone for the rest of the play. Once the witches become involved, the theme of "fair is foul and foul is fair" is seen in every corner of the drama. Shakespeare uses this theme to cast doubt on even the most noble of characters, especially in that Macbeth, a seemingly noble and devoted subject (and cousin and friend) to Duncan, is soon blamed for killing the King and of other terrible acts. The witches seem to call up this dark image, perhaps like a spell, and "command" that it hover through the air, where nothing is left untouched.

ALL:

Fair is foul, and foul is fair.

Hover through the fog and filthy air. (I.i.11-12)

When Macbeth enters the scene from the battlefield, he echoes the same words, perhaps showing how closely aligned he actually is to what the witches have planned for him: perhaps he is more willing than even he knows, seen especially in how quickly he accepts their prophecies.

MACBETH:

So foul and fair a day I have not seen. (I.iii.39)

Macbeth himself reflects this theme. He seems so "fair" in that he is such a hero, supportive of Duncan, and loved by Duncan. No one would, at the place's start, question Macbeth's loyalty, yet this quickly changes. He represents what seems fair ("good") and what is really foul ("evil").

When Duncan enters the courtyard of Inverness (Macbeth's castle), he comments upon how lovely it is. He has no way of knowing that what seems so fair will actually be the last place he lives to see. No one would suspect it for the castle and the air are so fine.

DUNCAN:

This castle hath a pleasant seat; the air

Nimbly and sweetly recommends itself

Unto our gentle senses. (I.iv.1-3)

When Macbeth hires the men to kill Banquo, he presents Banquo as "foul," blaming the murderers' disappointments in life on Banquo. The truth is that Banquo is the good one and Macbeth has caused their hardships, but the truth becomes cloudy, as if the air truly is "foggy and filthy."

When Macduff has had enough of Macbeth's treachery, he travels to England, where Duncan's son Malcolm, true heir to the throne, has taken refuge in the court of Edward the Confessor. However, because Macduff has left his family unguarded at home and comes from Macbeth's court, Malcolm distrusts Macduff, who is actually a very good man. Because of Macbeth's behavior, Macduff seems "evil," while he is actually a "faithful" and dedicated citizen of Scotland.

Malcolm, in order to test Macduff, presents himself as an evil man who would destroy Scotland, being a worse King even then Macbeth. In doing so, he pretends to be a threat to his homeland. When Macduff hears Malcolm's words, he believes that Malcolm is not fit to live, let alone to govern Scotland. As Macduff mourns the fate of Scotland, Malcolm realizes that Macduff is a good man. Very soon after, news comes that Macduff's family has been slaughtered at Macbeth's order, and Malcolm is further convinced that the man before him is as just and noble as he claims.

Of course, one would believe that being King and Queen would be wonderful for Macbeth and Lady Macbeth, but we soon see that their lives have deteriorated terribly, supporting this theme.

Once the words "fair is foul and foul is fair" are uttered by the witches, this theme works its way throughout the play, and it is not put to rest until the Macbeths are dead and Malcolm returns to the throne, where "God" has "ordained" he should be.

At the very opening of William Shakespeare's Macbeth, we see the three witches discussing where they will next meet. After they decide upon the heath, and just before they exit the stage, they say:

Fair is foul, and foul is fair:

Hover through the fog and filthy air.

In one way this can be interpreted as referring to themselves, that what they find fair or delightful is unpleasant or horrible to most people and vice versa. On another level though, it has broader implications for the play as a whole.

To a large degree, it talks about two things, first that appearances may be deceptive, that people who look fair on the outside or appear benevolent may be evil on the inside. Also, it suggests that whether something is fair or foul depends on perspective. In a battle, the outcome is always fair (in the sense of good) for the winner and foul (in the sense of bad) for the loser. 

On a more specific level, Macbeth, as we first encounter him in the play, is a loyal patriot and good soldier, a character who appears on the "fair" side of the comparison. The witches, though, intuit and manipulate his latent ambition so he gradually transforms himself from fair to foul over the course of the play.

In the first scene of the play, the Three Witches recite the phrase "Fair is foul, and foul is fair. / Hover through the fog and filthy air" (Shakespeare, 1.1.12-13). The denotative meaning of the phrase is that whatever appears to be appealing is impure and whatever appears to be impure is actually appealing. This phase is known as a paradox, a statement that contradicts itself but includes a hidden truth. It is also a motif, an object or idea that is repeated throughout a literary work in order to help develop a theme. The phrase essentially means that appearances can be deceiving.

There are numerous examples of deception throughout the play Macbeth, which correspond with the paradox "fair is foul and foul is fair." For example, Macbeth is fooled by the Three Witches into believing that the second set of prophecies are positive, which boosts his confidence and leads to his downfall. Characters throughout the play also utilize false appearances to deceive one another. King Duncan is fooled into believing that Macbeth is a friendly ally instead of a malevolent traitor. Macbeth also feigns friendship with Banquo before hiring assassins to murder him. Even Malcolm pretends to be a depraved individual in order to test Macduff's loyalty. Overall, Shakespeare portrays how appearances are deceiving throughout the play and utilizes the motif "Fair is foul and foul is fair" to develop this theme. 

At the beginning of Macbeth, the three witches offer the "fair is foul" paradox, which sets up the thematic foundation of the play. By saying that "fair is foul, and foul is fair," the witches challenge the characters and the audience to see that what appears as good on the surface may actually be negative underneath. For example, Macbeth appears as good--he is a valiant fighter in the name of King Duncan. However, soon he is taken over by his own greed and ambition and kills the king whom he once loved and honored.

In the paradox, the witches go on to say, "hover through the fog and filthy air," meaning that seeing the truth about someone's character is not simple and that one must wade through "fog and [filth]" to uncover the truth. For example, Macbeth kills Duncan early in the play, and he goes on to kill others. But the other characters do not immediately suspect him as a murderer because Macbeth still appears to be good on the surface. Banquo does fear that Macbeth may have done something immoral to rise so quickly to the position of king, but he needs to work through the facade that Macbeth has constructed to hide his devious acts. So, the witches' paradox relates to the theme of illusion versus reality that is constructed in the play.

In Act 1, Scene 1, the end of the witches' chant delivers a pronouncement that becomes emblematic for the rest of the play:

"Fair is foul, and foul is fair.

Hover through the fog and filthy air" (I.i.11-12).

Macbeth creates a dynamic theme through the interesting dichotomy between fair and foul.  Through the witches' first scene, the playwright suggests that appearances cannot be taken for granted.  Events or people who may seem to have the appearance of goodness cannot be trusted to be "fair," just as things that may be "foul" in appearance could very likely be benign or helpful. 

The witches' own predictions exemplify the theme of "fair is foul, and foul is fair" as their suggestions of Macbeth's rise to power have all the appearance of being wonderful; they cater to his ambition and pride, and suddenly he sees himself rising to the coveted position of Thane of Cawdor and even King of Scotland.  However, in hindsight, the audience or reader can understand that the witches' seemingly "fair" prophecy was actually meant for evil purposes: to tempt Macbeth toward corruption and deceit, leading him to terrible consequences. 

Macbeth echoes the witches' phrase the first time he speaks in act 1, scene 3. Following the battle, Macbeth and Banquo are traveling on the heath when Macbeth remarks, "So foul and fair a day I have not seen" (1.3.40). Macbeth finds the day "foul" because of the bloodshed and awful violence of the battles but also refers to the day as "fair" because of his impressive performance on the battlefield and notable victories. Macbeth and Banquo then interact with the nefarious Three Witches, who awaken Macbeth's ambition by addressing him as Thane of Cawdor and future king. Once Ross and Angus deliver their message and the first prophecy is confirmed, Macbeth immediately begins to entertain the idea of murdering King Duncan.

Verbal irony - wherein the words used convey a meaning different from the literal meaning - abounds in Macbeth, Shakespeare's paradigm of equivocation. Verbal irony achieves its finest expression in the riddling words spoken both by the three witches and Macbeth, himself, "Fair is foul, and foul is fair". These words form a kind of caption to the theme of the play: Nothing is as it seems. The world is topsy-turvy. High is low, and low high. Good is evil, and evil good. When in the  first few lines he remarks to Banquo, "So foul and fair a day I have not seen" (I, iii. 38), Macbeth is really giving voice to the dominant paradox of the world of play, expressed by the witches scant moments before.  "Fair is foul, and foul is fair". (I, i. 11). In other words, disharmony is the new normal. The world of the play is laced with antitheses which cancel each other out: At one point, night is "at odds with morning" so that  it is impossible to tell them apart; a battle's outcome is uncertain, like two swimmers who contend with each other in fatigue, and drink both "provokes" and "unprovokes" lechery. As much as the play tends toward disharmony, so does it 'wind down' toward entropy, not only in the suffering kingdom of Scotland, but in its disordered king whose nearly final words express an ennui unparalleled in Western drama:

It is a tale
Told by an idiot, full of sound and fury,
Signifying nothing.
(V,v. 26-28)

This phrase appears at the beginning of the play while the witches are planning to meet Macbeth for the first time after his victory in battle. In Act One, Scene 1, the witches recite the significant phrase, "Fair is foul, and foul is fair" (Shakespeare 1.1.12). This motif runs throughout the entire play and essentially means that appearances are often deceptive. Also, the word "fair" means good, and "foul" means evil. The witches are saying that things that seem to be good have the potential to be evil. This ominous phrase encourages the audience to perceive situations at a deeper level and not take character's actions or appearances at face value. For example, Macbeth believes that he is destined for greatness after hearing the witches' prophecy in Act One, Scene 3. However, Macbeth becomes ambitious and ends up killing King Duncan. Macbeth then begins his tyrannical reign and cannot stop murdering people that he considers adversaries. Macbeth's seemingly "fair" prophecy turns out to be "foul." 

The witches speak this line, in the first scene of the play. They have just announced their intention to "meet again," specifically with Macbeth, after the "battle's lost and won." We do not know what they have planned, but we can tell that they do not mean well, and that their meeting with Macbeth portends great evil. They fly away through a storm, chanting the rhyme mentioned in the question. This sets the stage for the play in an important way. The idea that things are not as they appear--that what appears to be fair is actually foul--is a running theme in the play. Macbeth's apparent loyalty to Duncan disguises his treachery, his ascent to the throne is built upon the murder of a most fair monarch, and Lady Macbeth casts aside her femininity--an act that would have been viewed as "foul" to Shakespeare's audiences--to plot the murder of Duncan. Moreover, the witches themselves offer up prophecies that seem very good for Macbeth, but are in fact ruinous.

In Shakespeare's Macbeth, the theme "Fair is foul and foul is fair" is expressed throughout the play's five acts.

The Weird Sisters (the witches) introduce the theme in the very first scene:

ALL:

Fair is foul, and foul is fair.
Hover through the fog and filthy air. (I.i.11-12)

At the play's beginning, the audience cannot be certain of the quote's meaning. We can assume that since witches are evil (something the Elizabethan audience believed completely), and they're preparing to meet with Macbeth, their words do not bode well. 

As Macbeth and Banquo come upon the scene, Macbeth refers to the fairness and foulness of the day: something that at first seems to refer to an impossible situation—for how can a day be fair (good) and foul (bad)?

MACBETH:

So foul and fair a day I have not seen. (I.iii.39)

The audience can infer that Macbeth is referring to the greatness ("fair") of the day because they have beaten the Norwegians in battle; when he comments that the day is "foul," he could be referring to the terrible weather or perhaps more likely, the many lives lost in the battle.

Soon after the witches deliver their predictions to Macbeth and Banquo, Macbeth receives the title of Thane of Cawdor, as the witches had predicted. Macbeth (at this point in the play) has sense enough to question what is happening.

MACBETH:

This supernatural soliciting
Cannot be ill, cannot be good. (141-142)

This comment appears to echo the "fair is foul..." theme: how can it be bad to be named the Thane of Cawdor (a gift from the king for Macbeth's valor on the field of battle)? At the same time, how can it be good in that the witches are involved? Nothing associated with witches is anything but evil.

In Act One, scene five, Lady Macbeth repeats the theme when she tells Macbeth to offer a "welcome" to Duncan in his speech and manner, but hide his true and deadly intent from sight. In other words, be as beguiling as a lovely flower, but as deadly as the snake that hides beneath it.

LADY MACBETH:

...bear welcome in your eye,
Your hand, your tongue; look like the innocent flower,
But be the serpent under't. (I.v.69-71)

In this way, Lady Macbeth warns Macbeth not to give any clue to anyone that they are plotting Duncan's murder.

The theme remains throughout the play. In Act Four, scene one, the witches tell Macbeth that he will be safe until the woods move to the hills, and that no man born of a woman can harm him. These promises are intentionally misleading, and Macbeth does just what the witches intend by misinterpreting their words as guarantees of his success. The predictions appear "fair" (good), but in Act Five, scene four, when Malcolm's soldiers use branches from Birnam Wood to camouflage themselves as they move to Dunsinane Hill, it appears as if the woods are moving—the once seemingly impossible situation by which Macbeth can be vanquished.

In Act Five, scene five, facing Macduff, Macbeth believes he cannot be beaten because all men are born of a woman; this "fair" (positive) fact gives Macbeth a false sense of security. However, when he discovers that Macduff was born by Caesarean section (C-section), which would not have been considered a natural birth, he realizes the promises the witches made were intentionally misleading ("foul").

In the end, Macbeth is undone by his belief in superficial appearances.

"Fair is foul and foul is fair" also refers to Macbeth's quest to be king. In order to be "fair" to Macbeth's talents and potential, he must have the opportunity to become king, at least according to Lady Macbeth and, later, Macbeth.  However, the murderous methods employed are a "foul" means to this goal.  In addition, the battle takes place in Dunsinane is "foul" as is all violence; however, in order to bring justice ("fair"), a battle must ensue to strip Macbeth of his tyrannical, murderous reign.

In the first act, the witches declare "Fair is foul and foul is fair" (Act 1, scene 1)and Macbeth remarks how the weather is "So foul and fair a day I have not seen" (Act 1, scene 3).  The witches are telling the audience that whatever good is bad and whatever bad is good.  This would set the tone for the rest of the play.  As for Macbeth's line, this is a example of foreshadowing.  He says this line before he and Banquo sees the witches and echoes what the witches say.  Also this line reminds us how the weather can mirror what is happening on stage.  In various parts of the play, characters will remark on the weather and it often reflects the state of the character or Scotland.

Shakespeare puts these words in the witches’ chant as part of setting the mise-en-scene for the play’s unfolding.  They are saying that the natural order of things is upset, that Nature herself is at odds with her own rules, her own “normal,” and  that likewise the human world is out of order and balance.  What should be a loyalty to his king becomes, for Macbeth, an unnatural ambition, and a bloody deed rather than the hospitality implied when Macbeth invites Duncan to Dunsinane, “fair” being turned into “foul.”   All is out of order.  Equivocation, the vagueness of a speech misinterpreted by the hearer, is the upsetting of language, the breakdown between what is meant and what is implied, such as “till Burnim Woods does come to Dunsinane” or “no man born of woman” (because Macduff was born by Caesarean section).  What appears as “A” is actually turned upside down to “non-A.”  “Fair” becomes “foul.”  The witches, with their super-human powers, see that the world is in a state of chaos now.  Shakespeare finds a perfect way and the perfect character to utter this phrase and warn the humans, who of course do not heed the warning.

"Fair is foul and foul is fair" establishes one of the main themes of the play and goes far deeper than simply trusting or not trusting in physical appearances. On one level, Shakespeare does say that we should not trust people simply based on their appearance. This is a major flaw in Duncan's character: he is too trusting and not able to discern enemies in his midst. This makes him susceptible first to Macdonwald's treachery and then to Macbeth's. But a deeper question the play asks is how to get to the reality that lies beneath appearance. Duncan, seemingly, has every reason to trust Macbeth fully: he is his cousin, and he has fought valiantly and beyond the call of duty to defeat Macdonwald and protect Duncan's reign. Why would Duncan have the least reason to suspect treachery? On the surface, none. However, had he gotten to know Macbeth beyond surface appearances, Duncan might have caught glimmers of the depth and hunger of Macbeth's ambition—his dark side—and known to take precautions.

The most important incident of "fair is foul" is Macbeth's taking of the throne. This act looks "fair" (desirable) to him. It is everything he has ever dreamed of, the culmination of all his ambitions. Yet, that seemingly "fair" prize turns out to be "foul." Macbeth derives no joy, but only pain, fear, and a deadening of conscience from achieving his ambition. As is said early in the play, just getting the outer garments of a position, such as a crown, doesn't make a person inwardly fit to rule. The play suggests that having a moral compass helps us to discern between fair and foul and that we should not be deceived by temptations from the dark side. What should have alerted Macbeth to the foulness of the witches' prophecies was not their outward appearance but their connection with the supernatural power of darkness and the way they dangled before him his deepest desire.

It implies that things are not always what they first appear to be.  You could just about apply this line to any murder mystery that you have ever seen.  The murderer is always the person that you least suspect.  Good is bad, and bad is good.  

Macbeth first appears to be good.  He's honored by King Duncan for his prowess in battle and major contribution to the overall victory.  But as the play continues, it is clear that Macbeth is indeed not nearly as fair as he first appeared.  Conversely, Lady Macbeth is evil at the start of the play.  Some readers even think that she deserves more blame than Macbeth himself.  But I do want to give her some credit.  Her guilt absolutely consumes her.  She doesn't turn from foul to fair and pure as the driven snow, but at least she expresses a hefty amount of remorse.  

The line also implies to the audience that they just shouldn't trust what the witches say word for word.  Macbeth learns that one the hard way when Birnam wood comes marching to his doorstep and Macduff is able to kill Macbeth because Macduff wasn't "born" in the traditional manner.  

"Fair is foul and foul is fair" relates to the witches' prophecies because it is a statement of paradox and inversion. The prophecies are true, but only in part, and end up being to MacBeth's detriment and final demise. MacBeth believes the prophecies to entirely be true, but doesn't get the fact that foul is fair and fair, foul. He takes the prophecies as literally true. He doesn't see that he is the foul one, and that when the witches say "something wicked this way comes," they're talking about what he's become. You have it mostly correct, however. The statement is about appearances and reality, but also about how these two can change. MacBeth is heroic soldier at first, but becomes "foul." Lady MacBeth is strong and vicious at first, but becomes mad later.