What do the words, "Fair is foul, and foul is fair" from Macbeth mean? How is this an example of verbal irony?

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Michael Otis eNotes educator| Certified Educator

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)