Shakespeare develops Macbeth's internal conflict through the use of dramatic monologue, particularly in Act I, scene vii as he debates the decision to murder Duncan. Macbeth worries over his familial connection to Duncan as well as his role as Duncan's host:
"He's here in double trust:
First, as I am his kinsman and his subject,
Strong both against the deed; then, as his host,
Who should against his murderer shut the door,(15)
Not bear the knife myself" (I.vii.12-16).
Macbeth's moral side forces him to question his reasons and motives for planning Duncan's death; he realizes that he has no clear motive, only his ambition to usurp the throne. Macbeth's ambition and desire to be king pushes him to take action that he would normally never consider:
I have no spur(25)
To prick the sides of my intent, but only
Vaulting ambition, which o'erleaps itself
And falls on the other— (I.vii.25-28)
This quote in particular illustrates Macbeth's genuine conflict over the plot to murder Duncan; he fears the consequences of that his actions will bring, but his "vaulting ambition" furthers his drive to murder the king and take his place.