Conditional sentences can be divided into true conditional sentences and false conditional sentences. A true conditional sentence means that the events described in the sentence are facts or things that the speaker seems to be able to achieve. Unreal conditional sentences represent things whose conditions are contrary to the facts or impossible to realize, which is what we call subjunctive mood.
The first example is that if he comes, he will call me. This sentence is a statement of the fact that he will come, but he will definitely contact me when he comes. This is a real conditional sentence and should follow the principle that the subject is subordinate to the subject.
If I were you, I would hit him. If I were you, I would hit him. Obviously, I can't be you. This is an invalid conditional sentence. We should follow some principles of subjunctive mood.
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