What is the Sequence of Tenses?

The sequence of tenses explains why subjunctives in subordinate clauses are in the tenses that they are in, and it provides insight into how to translate the clause. Latin has two sequences of tense- primary and secondary.

The primary sequence includes forms of the indicative whose action is not yet complete. The secondary sequence, also called "historic", includes forms of the indicative whose action is complete.

Subjunctives in primary and secondary sequence are determined by two things: whether the verb in the main clause is primary or secondary, and whether the action of the verb in the subordinate clause is seen as being accomplished before or at the same time as the action of the verb in the main clause.