Dramatic ironies in Macbeth?
And can you please explain them?
1) When Macbeth says in Act V: "Doctor, the thanes fly from me/ Come, sir, dispatch. If thou couldst, doctor, cast/ The water of my land, find her disease,/ And purge it to a sound and pristine health" (V, ii, 49-52).
2) "We might have met them dareful, beard to beard,/And beat them backward home" (V, v, 6-7).
Dramatic irony is a literary resource through which the audience knows more than the character or characters involved.
Macbeth is riddled with dramatic irony from the very beginning. One outstanding example occurs in Act II, scene iii. We have listened to Macbeth and his wife plotting Duncan's murder and carrying it out. Yet in this scene the other characters -Macduff, Lennox, Banquo, and Ross- genuinely believe that the regicide was committed by the drunken guards that Lady Macbeth smeared with Duncan's blood. The only ones who suspect foul play, but are unsure of its source, are Duncan's sons. We find another interesting example in Act III, scene i, when Macbeth has already planned Banquo's murder and yet tells his unsuspecting victim that "we should have else desired your good advice [...]" In brief, Macbeth tells Banquo that he would prefer him to stay when all along he has counted on his riding away to have him waylaid and killed. The audience is forewarned, yet Banquo does not know he is riding to his death.
In your first quote, the dramatic irony lies in the fact that Macbeth knows exactly what ails his wife, and so do we: the crimes she has connived at are affecting her sanity. The doctor is not aware of this. This particular quote has been the subject of much controversy, since many experts maintain that Macbeth is in fact asking the doctor to allay his wife's suffering by giving her a deadly potion.
Your second quote shows Macbeth pretending surprise at his former friends and allies having joined the invading army. I would not call this dramatic irony, since both the characters involved and the audience know the reasons for the defection. Seyton, his interlocutor, has chosen to side with Macbeth, but it cannot have been an innocent choice after it was public knowledge that Macduff's family was killed following Macbeth's orders.