How is Capulet impulsive in Romeo and Juliet?

Like most Shakespearean characters, Lord Capulet is complex and very human. Early in the play, Lord Capulet appears to be a jovial, sensible father and husband, but as the story unfolds, it seems clear that he is prone to wild mood swings and impulsive behavior.
When Paris approaches him to ask permission (or at least discuss the possibility) to marry Juliet, Lord Capulet seems like a reasonable man. He tells Paris, "Let two more summers wither in their pride / Ere we may think her ripe to be a bride," and he suggests that Paris "woo" her because he believes Juliet should have a say in whom she marries. He's as protective of his daughter as any father would be.
Likewise, when Tybalt sees Romeo at the Capulet feast, he wants to kill him on the spot, but Lord Capulet counsels temperance and practicality. This act prevents a major Montague and Capulet confrontation and serves to keep the peace.
We begin to see over the course of the story, though, that when his authority is challenged in any way, Lord Capulet becomes childish and impulsive. Just hours after Romeo kills Tybalt, Lord Capulet is ready to marry Juliet to Paris almost immediately without considering any of the consequences for Juliet (among others). It seems clear from the text that his hatred for the Montagues leads him to rash and sometimes unjust decisions.
Another example: he becomes enraged when Juliet refuses to marry Paris, and some scholars believe that when he says, "My fingers itch," he is thinking of doing physical violence to Juliet. This contrasts sharply with the calm, temperate, loving father we see in the beginning.
As Shakespeare so often does, he strips away the artifice and allows us to witness the emergence of a character's true nature.