Prior to the Witches greeting Macbeth, I personaly believe that he had no intention of being king. Through Act 1 scenes 1-7 Macbeth reapeadily states that he thought Duncan was a very wise king, that doesn't abuse his powers over the people. Not to mention, Macbeth was shocked, when the witches greeted him as Thane of Crawdor and then as a king. He didn't believe a single word og what the witches said until the messengers arrived and granted him his brand new