The past subjunctive: que tu sois venu

The past subjunctive is the subjunctive for an event that is already over: Je suis content que tu sois venu. - I am glad you came. It is the present subjunctive of avoir or être plus a past participle. The triggers are the ones you know; only the timing is new.

Necessity, doubt and emotion and the conjunctions decide whether you need a subjunctive. This page decides which one.

How to form it

Take the passé composé and put its auxiliary into the present subjunctive.

The glosses: that I did, that I left, and so on down. Watch the avoir column: it has no r anywhere and no i after the y (ayons, ayez), and il takes ait, never est.

The auxiliary choice and the agreement are the passé composé's:

The one question: is it over?

The trigger tells you to use a subjunctive. It does not tell you which. One question does: is the event in the que clause already over?

The glosses, row by row: she has to leave / she has to be gone by noon; although she works hard / although she worked hard; I am sorry he is leaving / I am sorry he has left.

Without the past subjunctive each pair would collapse into one sentence. The tense of the clause is what says when.

Avant que: the deadline

Avant que always takes the subjunctive, because its event has not happened yet. The past subjunctive still has a job here: it says the event will be finished by the deadline.

• Partons avant qu'il arrive. - Let us leave before he arrives.
• Partons avant qu'il ait fini son discours. - Let us leave before he has finished his speech.

Learn one phrase whole: avant qu'il soit trop tard - before it is too late. You will also see it with a ne that negates nothing, the ne explétif: avant qu'il ne soit trop tard. The conjunctions page covers it, and jusqu'à ce que (until) works the same way.