The greatest fear of Jonathan is the love he feels for his sister.

But isn't that what love is, Clarissa? Ownership? 'I am my beloved's and my beloved is mine,' as the Song of Songs goes."
"No. And don't quote the Bible at me. I don't think you get it...It's not just that someone belongs to you, it's that you give yourself to them. I doubt you've ever given anything to anyone. Except maybe nightmares."
"To give yourself to someone?" The thin smile didn't waver. "As you've given yourself to Jonathan?"
"What?"
"You think I haven't seen the way you two look at each other? The way he says your name? You may not think I can feel, but that doesn't mean I can't see feelings in others.

Yes," Jace said, "I regret having disobeyed you."
No! Clary thought, but her heart sank. Was he giving up, did he think it was the only way to save her and Simon?
Valentine's face softened. "Jonathan-"
"Especially," Jace said, "since I plan to do it again. Right now.

And next time you're planning to injure yourself to get me attention, just remember that a little sweet talk works wonders.

Valentine!"
"You mean father. I despise this modern habit of calling one's parents by their names."
"What I want to call you is a hell of a lot more unprintable than your name."
- Clary Fray and Valentine Morgenstern (City of Ashes)

Yes," Jace said, unable to help himself, "I was trained to be an evil mastermind from a young age. Pulling the wings off flies, poisoning the earth's water water supply - I was covering that stuff in kindergarten. I guess we're all just lucky my father faked his own death before he got to the raping and pillaging part of my education, or no one would be safe.