1. If it rains tomorrow, I will not start.
2. If it should rain tomorrow, I will not start.
3. If it rained tomorrow, I would not start.
4. If it rained yesterday, he didn't go to work.
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Are they all grammatical? Which ones are not grammatical?
3 is not right. The other three sentences are grammatical.
Let's analyze each sentence to determine if they are grammatical:
1. If it rains tomorrow, I will not start.
This sentence is grammatical. It follows the pattern of a conditional statement using the present tense.
2. If it should rain tomorrow, I will not start.
This sentence is also grammatical. The addition of "should" in this sentence indicates a slight possibility of rain, but the structure of the sentence remains intact.
3. If it rained tomorrow, I would not start.
This sentence is not grammatical. The verb tense usage is incorrect. The word "rained" suggests past tense instead of future tense.
4. If it rained yesterday, he didn't go to work.
This sentence is grammatical. It correctly uses the past tense for both the condition (rained) and the result (didn't go).
To summarize: Sentence 3 is not grammatical, while the remaining sentences are grammatical.