WISH / IF ONLY

We can make second and third conditionals more emphatic by placing only after if:

If (only) I knew the answer, I'd tell you.
If (only) I had revised more, I would have done better on my exam.

If only can be replaced with I wish, and the main clause can be omitted:

I wish I knew the answer.
I wish I had revised more.

Patterns introduced with I wish... are used to express wishes about the present, past and future.