how does macbeth interpret the prophecies pronounced by the first three apparitions?

Question

macbeth act 4 

Answer 1

The prophecies are of the form "x will not happen unless y happens" and in each case y is a seemingly improbable event.  E.g. "no one will kill you unless that person is not of woman born" or "you won't  be vanquished until Birnam wood comes to Dunsinane hill".  So he interprets this to mean x will never happen since it seems that y will never happen.