One of my students wrote:
I hope you could.
he was supposed to write
I wish you could.
Should I accept his sentence? Is it grammatically correct?
Thanks a lot.
No. Hope uses present tenses (except when you're talking about the past obviously), wish uses past. It's like the difference between 1st and 2nd conditional - one is possible/probable (present tense) and one is impossible/improbable (past tense)
I wrote a thesis about all this once. When we talk about genies giving us "3 wishes" we'd be better talking about "3 hopes"! They're going to happen, they're not hypothetical.