This question, actually is one that is very much debated in regards to this play. In order to answer it satisfactorily, you must define "to blame." Do you mean who actually wielded the knife? No question, then, it's Macbeth himself. Though we don't see the murder onstage, he and Lady Macbeth have a scene -- Act II, scene ii -- in which Macbeth has just come from the murder.
However, "blame" is often distributed, in a murder, to those who function as accessories to the crime. In this case, is Lady Macbeth also "to blame?" How about The Witches? Let's look at both of these possibilities individually.
First, Lady Macbeth, in the scenes before the murder, seems to drive the action forward. In Act I , scene v, she all but declares the murder a...
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