Looking on the internet deeply has found these results:

I would but I can't is the most popular phrase on the web.

I can do but I can't 15 results on the web	I would but I can't 1673,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I can try, but I can't promise anything. I do but I can't say. But I can't rely on just that. But I can't just go home and forget about it. I do but I can't say. I'm sworn to secrecy. I really do but I can't right now. I can do baby, or I can do geezer murder mystery but I can't do both. I do what I can for that boy, but I can't ben him all the time.	I would, but I can't this time. I would, but I can't deny I'd prefer one of my own. I would've, but I can't get a hold of him. I would, but I can't look at you when I'm sober. If I could, I would, but I can't fly around looking for red roofs and lavender. Just Leave. I would but I can't be sure you won't call the police. If I could sing a lick, in any human way possible, I would, but I can't. I would but I can't be sure you won't call the police.

I can do but I can't

15 results on the web

I would but I can't

1673,000 results on the web

More popular!

I would, but I can't this time.
I would, but I can't deny I'd prefer one of my own.
I would've, but I can't get a hold of him.
I would, but I can't look at you when I'm sober.
If I could, I would, but I can't fly around looking for red roofs and lavender.
Just Leave. I would but I can't be sure you won't call the police.
If I could sing a lick, in any human way possible, I would, but I can't.
I would but I can't be sure you won't call the police.