Dramatic irony is a kind of irony that arises when there is some information that the reader or the audience knows but one or more characters in the play are completely unaware of. Use of such a literary technique produces a mixture of suspense, confusion and excitement as the readers or the audiences await certain things to happen based on the extra information they possess, but the reaction of the characters is sudden and unpredictable. William Shakespeare’s Macbeth is full of powerful rhetorical techniques, including dramatic irony. Let us look at a few examples.
In Act 1 Scene 3, Macbeth says he cannot be the Thane of Cawdor and gets surprised by what the witches tell him. He is not aware of the fact that the king has already decided to give him this position. This is a clear case of dramatic irony as there is disagreement between a character’s speech and actual events taking place in the play.
By Sinel's death I know I am Thane of Glamis;
But how of Cawdor? The Thane of Cawdor lives,
In Act 1 Scene 4, King Duncan considers Macbeth to be very trustworthy and loyal, but the audience already knows that Macbeth will betray the king.
There's no art
To find the mind's construction in the face:
He was a gentleman on whom I built
An absolute trust.
Another example is in Act 1 Scene 6 when Duncan says that he finds Macbeth’s castle a pleasant place and the air smells sweet and light.
This castle hath a pleasant seat; the air
Nimbly and sweetly recommends itself
Unto our gentle senses.
Discussion about the pleasantness of the place, beautiful weather, etc. is very ironic as the king Duncan isn’t aware of the violence and unpleasant events that will likely happen just after this. We know that because of the witch’s prophesies Macbeth plans to murder King Duncan and acquire his throne. It is from the soliloquies that Macbeth had just delivered, the audience clearly knows what no other character in the play, except Lady Macbeth, knows. Hence, audience is aware of Macbeth’s real intentions but the king isn’t.
In Act 4 Scene 1, the second apparition makes Macbeth believe that he cannot be killed.
The power of man, for none of woman born
Shall harm Macbeth.
But we know that there is something hidden from Macbeth here. He will be killed by Macduff, who was born by a caesarean section.