"Macbeth" is the last of the four tragedies written by Shakespeare. It is about Macbeth, a powerful hero, who sinks into a tyrant. In the play, "Fair is foul, and foul is fair", is a famous quote, it comes at the very start of the play, and it shows that the dialectical relation between foul and fair. Shakespeare expresses that it is difficult to tell appearance from reality by examining reversal in Macbeth, witches’ predictions, Duncan’s death, Lady Macbeth’s change and witches’ fair and shows that everything is not always as it seems.
  First, Shakespeare shows Macbeth’s reversal and predictions by using comparison. The comment "Fair is foul, foul is fair" may predict the moral reversal of Macbeth in the coming course of the play, his move from hero to murderer.  This comparison can be found in Act3 Scene4 "Blood will have blood."(p99, 123) In Act1 scene3 (p17, 67), the witches predict that Macbeth can be the king and Banquo’s son will be the king. It is obvious that Macbeth becomes the king, the first prediction is true, but at the end of the play, Malcolm is the king. So the second prediction is false. One of the predictions is true while the other is false. Shakespeare uses comparison to show reality versus appearance.
  Furthermore, Shakespeare shows things are not what they seem by irony in Duncan’s death and the huge change in Lady Macbeth. In Act1 Scene 6, when Duncan visits Macbeth's castle, he says "see, see, how honored hostess!" (p35, 10) Later, he is killed by Macbeth. It suggests that everything has different aspects, meaning that things that appear positive can often have negative aspect. Appearance may be opposite to reality. In Act 5, Scene 1, Lady Macbeth said, "Out, damned stop! Out I say! "And continued with, "What, will these hands ne’er be clean?" (p149, 35)This is definitely ironic, because at first in the play Lady Macbeth dispels Macbeth’s concerns with little thought, and later Macbeth would expect her not to think of them.