Sequence of Tenses - Concordance des temps
When speaking French (or any other language), it is important to use the correct sequence of tenses. In complex sentences, there is a relationship between the verb in the main clause and the verb in the subordinate clause. Using the correct sequence of tenses is just as important as conjugating the verbs correctly and using the appropriate mood.
For exemple, in French you can't say "Je ne savais pas que tu es étudiant" - you have to say Je ne savais pas que tu étais étudiant. Likewise, in English, you would say "I didn't know you were a student" rather than "I didn't know that you are a student." Because the verb in the main clause is in the past, the verb in the subordinate clause must be in the past as well.
Note that the sequence of tenses for subordinate clauses is identical for main clauses in the present and future.
*These literary tenses are nearly always replaced by their non-literary equivalents. The literary tense is the "official" tense to be used in the construction, but in reality the imperfect subjunctive and pluperfect subjunctive are obsolete in spoken French and rare in written French.。