In the first scene Capulet addresses Paris (who is asking to marry Juliet for the umpteenth time) and seems just to be trying to get rid of him and get him off his case:
But saying o'er what I have said before:
My child is yet a stranger in the world,
She hath not seen the change of fourteen years;
Let two more summers wither in their pride
Ere we may think her ripe to be a bride.
Juliet, he says, is too young to marry. And later in the same scene, his crux argument is this:
But woo her, gentle Paris, get her heart;
My will to her consent is but a part.
An she agree, within her scope of choice
Lies my consent and fair according voice.
In short, it's Juliet's choice: and Capulet's "consent" goes with Juliet's choice. But do we believe him? Well, by Act 3, once Tybalt has died (and, it might be said, the Capulet family significantly weakened), Capulet is telling Paris
I think she will be rul'd
In all respects by me; nay more, I doubt it not...
She shall be married to this noble earl.
Suddenly, Juliet is to marry Paris. And when she disagrees, Capulet loses it:
An you be mine, I'll give you to my friend,
An you be not, hang, beg, starve, die in the streets.
Capulet started by arguing it was Juliet's choice. He finishes up making a very firm decision himself. Has he changed his mind? Or has he just shown his true colours? Who knows - though my bet is on the latter.