First, sentence 1. is incorrect. You should replace 'would' with 'will', like this,Originally Posted by Unregistered
If I have time, I will help you.
Sentence 1. is an example of the 1st conditional:
If + Present tense verb + will
Second, sentence 1. refers to the Present. The speaker is saying that if s/he can find the time to help you, then s/he will definitely help you. Sentence 2. refers to the past. The speaker is saying that s/he has already decided that s/he doesn't have the time to help you, so s/he can't help you, but if she did
(Past tense) have the time, then s/he would (Past tense) help you.
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