The scary thing about Lord Capulet is that it isn't, at all, a gradual change. At the very start of the play, he's putting across that he's a jovial, avuncular old father, who puts his daughter's wishes at the very top of his list of priorities:
The earth hath swallow'd all my hopes but she,
She is the hopeful lady of my earth:
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.
She is the "hopeful lady of his earth" - she is the most important thing, the most hopeful thing to him in the whole world.
That, at least, is what he says when the play seems like a comedy - before, that is, Mercutio dies, and the whole thing twists into tragedy. Then, suddenly, he changes his mind entirely, on the night of Tybalt's death:
Sir Paris, I will make a desperate tender
Of my child's love: I think she will be ruled
In all respects by me; nay, more, I doubt it not.
And then, moreover, by the end of that evening, he's entirely denounced his daughter, thrown caution to the wind and told her that, if she doesn't marry Paris, she can get out of his house:
Thursday is near; lay hand on heart, advise:
An you be mine, I'll give you to my friend;
And you be not, hang, beg, starve, die in
For, by my soul, I'll ne'er acknowledge thee,
Nor what is mine shall never do thee good:
Trust to't, bethink you; I'll not be forsworn.
So the change is there in the language - as it always is in Shakespeare. Capulet's mind changes entirely.
The change in the way that Lord Capulet feels about his daughter is seen when you examine two different scenes. The first is Act 3, scene 5, when Lord Capulet and Lady Capulet are speaking to Juliet about a sudden change in the marriage plans between their daughter and Count Paris. Juliet tells her father that she has absolutely no interest or intent to marry Paris and basically tells him that she hates who she is when she says,
“Not proud you have, but thankful that you have.
Proud can I never be of what I hate,
But thankful even for hate that is meant love.” (A.3, s.5, lines 149-150)
Lord Capulet’s response is extremely overwhelming and he tells her that if she does not marry Paris and do what he wants her to do then he will drag her out of the house and basically have her executed, when he says,
“But fettle your fine joints 'gainst Thursday next
To go with Paris to Saint Peter's Church,
Or I will drag thee on a hurdle thither.
Out, you green-sickness carrion! Out, you baggage!
You tallow-face” (A.3, s.5, lines 156-160)
He continues by calling her nasty names and storms out of her room.
However, after Juliet is found dead in her room by the Nurse in Act 4, scene 5, he proves that he really does love her when he can not even speak after finding out about her death.
“Death, that hath ta'en her hence to make me wail,
Ties up my tongue and will not let me speak.” (A. 4, s.5, lines 34-35)
He continues in this scene by being upset and overwhelmed by her death. Additionally, at the end of the play he and Lord Montague are so stricken by the deaths of their children that they resurrect golden statues of the two in Verona.