If I study tonight, I can relax Saturday.
I can only find "could" used as a conditional. I'm not sure why can isn't one too. (I'm working my way through a 30-page .pdf on conditionals as I write this, and I *will* finish reading it, so maybe it'll become clearer then--but I'm impatient now. And there are so many smart and helpful people on this message board .)
I'm still working on understanding the first, second, third, and zero conditionals.
I just realized that in my example sentence, "can" is not a conditional. It expresses ability. Maybe that's why I couldn't find can used in this format in my explanations of conditionals.
1.If (provided (that)/assuming (that)/as longas/etc) I study tonight, ....
....I will/may/can/ take it easy on Sunday.
.... I'm taking it easy on Sunday
... I'm going to take it easy on Sunday.
2. If you will study tonight, I'll let you go to the party tomorrow.
3. If you're going to study tonight, I'll go out with Charlie.
4. If you're studying tonight, I'm going out with Charlie.
5. I'll fail the test unless I study tonight.
There are countless other possible conditional sentences. The one most commonly given as as example of the first conditional is if + present, will:
If I study tonight, I'll (I will) take it easy on Sunday.