Analyse and compare the exchange between Macbeth and Banquo in Act 2, Scene 1 with Banquo's speech in Act 3, Scene 1.
I dreamt last night of the three weird sisters:
To you they have show'd some truth.
(Act 2, Scene 1)
Macbeth and Banquo agree to discuss the issue of the witches and their prophecies at a later date: though, interestingly, Shakespeare never actually shows us the discussion, if it happens. The key point to take from this scene though, is in its first line - Banquo announces himself as "a friend", and thinks (of course, wrongly, for Macbeth is about to do the murder!) that he and Macbeth are a team, who will respond to the witches' prophecies as one.
What Act 3, Scene 1 shows us is Banquo thinking very much as an individual and seriously suspecting Macbeth and his motives:
Thou hast it now: King, Cawdor, Glamis, all
As the weird women promised, and I fear
Thou play'dst most foully for't...
Moreover, the pure-white Banquo of the earlier scene is also shown in this scene to be ambitious: the seed of greedy ambition is growing in his head as it did in Macbeth's.
If there come truth from them
As upon thee, Macbeth, their speeches shine
Why, by the verities on thee made good,
May they not be my oracles as well
And set me up in hope? But hush, no more.
And then Banquo falls silent. What was he going on to say if he had not been interrupted? Perhaps the key point to make in comparing these two scenes is that, though Banquo and Macbeth seem similar in the first, they become worryingly alike in the second!