I began recently to study English conditional sentences and now I'm trying to find information about Past Real Conditionals formation (as I understood, they are also called Zero Conditionals in other classification). There is not much info on the Web on this theme so I write here.
As I understand now, in either of the clauses - dependent(condition) clause and main(result) clause - we can use in any combinations:
- verb in any past tense (i.e. Past Simple, Past Continuous, Past Perfect, Past Perfect Continuous)
- constructions of type: modal auxillary verb + infinitive of main verb, with infinitive being able to express any aspect (i.e. we can use bare infinitive and various infinitival constructions like, for example, "be being written", expressing continuous aspect in passive voice, "have been writing", expressing perfect continuous aspect in active voice, etc.)
Please, let me know if it is right, and, in particular, provide me with some examples of sentences, which don't have the most obvious variant of structure in which both dependent and main clauses have verbs in Past Simple tense. The more nontrivial examples are, the better it will be.