What part of the play can the last line be linked to and what meaning can it represent?the line is as follows: "That function is smothered in surmise, And nothing is, but what is not."
Shakespeare loved antithesis. He loved to pit ideas against each other and see what happens. Macbeth is full of antithesis. In the very opening scene we are told that "foul is fair and fair is foul". In other words, things aren't what they appear to be.
Throughout the play, we are confronted with what something appears to be and reality. Macbeth appears to be a hero but proves to be a villain. Malcolm appears to be inept in battle but proves to be a crafty soldier. It appears that fathers are killed by their sons but it proves to be the handiwork of Macbeth. It appears that Banquo is Macbeth's friend but Macbeth proves to be an enemy.
Macbeth is a play where what you see is not what you get because "nothing is but what is not".
This line relates to the prophecy that the witches set up early in the play. The witches often speak in seeming riddles that set up paradoxes in the play. The line means that nothing is at it seems to be; Lady Macbeth tells her husband that he must have a "false face" to hide what his "false heart" knows so that everyone on the outside of their scheme does not suspect their true intentions. Much of the play functions in this manner as Macbeth hides his true intentions from his court and even eventually from his wife. Macbeth proves to be most unworthy of the role of king even though he commits many crimes to maintain his position.