No one uses the present subjunctive with "if" any more, as in Shakespeare's "If music be the food of love, play on." Ditto for the future, in which case the present tense would be used anyway. Even the past subjunctive is a bit of an endangered species, but it is formally used with a conditional construction when the premise is contrary to fact: "I wouldn't do that if I were [past subjunctive] you" -- I am not in fact you. "He didn't know that I was [past indicative] coming" -- I was in fact coming.

We use 'if' in the Conditional Sentences, for example: If you work hard, you feel tired. - Type 0 If it rains, I won't take a dog for a walk. - Type 1 If I won a lottery, I would buy a bank! - Type 2 If they had come earlier, they would have gone by train. - Type 3 if = 如果

Hi Rebecca, here is a recap: Conditional Sentence Type 1 → It is possible and also very likely that the condition will be fulfilled. Form: if + Simple Present, will-Future Example: If I find her address, I’ll send her an invitation. Conditional Sentence Type 2 → It is possible but very unlikely, that the condition will be fulfilled. Form: if + Simple Past, Conditional I (= would + Infinitive) Example: If I found her address, I would send her an invitation. Conditional Sentence Type 3 → It is impossible that the condition will be fulfilled because it refers to the past. Form: if + Past Perfect, Conditional II (= would + have + Past Participle) Example: If I had found her address, I would have sent her an invitation.