Why are there three witches in "Macbeth"?

The number 3 has, historically, always had a magical quality. The number appears many times throughout the play; 3 witches, 3 prophecies, 3 apparations, etc. The "temptation" scene is even the third scene of Act I, and the wiches tend to repeat the same thing, saying it "thrice". I really like Roman Polanski's version of Macbeth and his interpretation of the three witches; it is very druidic. There's 2 older ones and one younger one, almost like the  "witch in training. ' He also presents one witch whose eyes are covered (or maybe aren't even there!), one with her ears covered and the third one does not speak...is it a suggestion of see no evil, hear no evil, speak no evil??? Interesting interpretation, nonetheless.

The three witches in the book was used to represent the three Fates of the ancient mythology, who impersonally weave the threads of human destiny. They take in delight in their power of foretelling the future to play and toy with human's feelings and later destroy them.

'Witches' is ambiguous. Confusion has largely arisen because the Folio text refers to them in stage directions and speech prefixes as 'witches'. They call themselves the 'Weird Sisters' and...

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