Critically discuss the theme of ambition in Macbeth.
Ambition is, of course, one of the central themes of this play. You have picked a very broad topic, but there is one central question that you need to consider before you can move on. You need to decide whether Macbeth was an evil character with ambitions to kill Duncan before meeting the witches or whether it is the interference of the witches that prompts Macbeth to take the path he chooses.
Examining Act I we are presented with many different impressions of Macbeth. He is presented as a loyal and brave soldier, full of valour and having accomplished great deeds on the battlefield. At the same time, these deeds are presented as violent, and we are left to question whether this violence hints at something slightly perverse.
Also, Lady Macbeth describes her husband as being "too full o'the milk of human-kindness", which is a negative aspect in her eyes. This is something that she sees as a weakness, and perceives that she must overrule her husband's weaker side by her force of will. We see as well that when Macbeth does have second thoughts it is his wife that cajoles him on and forces him to continue with their plan.
Yet at the same time Macbeth is very open and honest about the role that his ambition plays, and wary of its dangers:
I have no spur
To prick the sides of my intent, but only
Vaulting ambitoin, which o'earleaps itself
And falls on th'other -
Macbeth is well aware of the dangers of giving in to ambition, but once he has set himself on this path, he cannot turn back - blood begets blood, and his conscience tortures Macbeth with his actions.