search by....themes - ambition Macbeth's ambition is in place before the play begins, but needs the suggestion from the witches and encouragement from his wife (no less ambitious) to spur him to action:

act one - scene three	Banquo asks Macbeth about his reaction to the prophecy
act one - scene five	Lady Macbeth fears the obstacles to Macbeth's ambition
act one- scene seven	Macbeth reflects on the unfairness of his ambition