After "si", which tense do you use in French?

Why the conditional is banned after si, the four hypothetical systems and the two real exceptions.

After a conditional "si" in French, the conditional tense is banned, and the reason is chronological, not aesthetic. Four tense combinations cover almost every case, two exceptions do allow the conditional, and a 2009 study of 120 speakers shows that spoken French is looser than the rule.

Why is "si j'aurais" wrong?

Because the condition comes before the consequence. The Vitrine linguistique of Quebec's language office puts it plainly: the condition, coming before the consequence, "ne peut être qu'au passé ou au présent (et non au conditionnel ou au futur)", while the consequence can only be in the future.

English speakers have an unfair advantage, because the same constraint exists in their own language. "If I would have known, I would have said something" is stigmatised in English exactly as "si j'aurais su" is in French: the hypothetical marker belongs in the main clause, not in the "if" clause. Map French onto that instinct and the rule costs nothing.

One landmark is enough: one "rais" ending per hypothetical sentence, never after "si".

What are the four systems with "si"?

The tense agreement handout from the Centre collégial de développement de matériel didactique lists four, and they cover nearly everything you will say.

Likely condition: si + present or perfect, main clause in the future. "Nous quitterons le port si la mer est haute."
Unreal in the present: si + imperfect, main clause in the present conditional. "Vous comprendriez mieux si vous lisiez le texte en entier."
Unreal in the past: si + pluperfect, main clause in the past conditional. "Vous auriez mieux compris si vous aviez lu le texte."
"Si" meaning "when" or "whenever": both verbs in the same tense. "Si tu as escaladé l'Everest, moi, j'ai marché sur la Lune."

The alignment with English is almost one to one: the second system is "if I read it, you would understand", the third "if you had read it, you would have understood". One difference matters: French uses a plain imperfect where English keeps a past subjunctive ("if I were you"). French says "si j'étais vous".

The office adds a useful variant: after a pluperfect, the main clause can stay in the present conditional when the consequence still holds today. "Si tu étais déjà allé à Londres, tu comprendrais" is about now.

When is the conditional correct after "si"?

There are two cases, and they explain sentences in official letters that look like mistakes.

The first is the "si" of indirect questions. When "si" introduces a reported question rather than a condition, the conditional comes back: the office quotes "Nous aimerions savoir si vous seriez disposée à entrer en fonction le mois prochain." That is "we would like to know whether you would be willing", and the test is the same: if "whether" works, it is not a condition.

The second is concessive "si", which grants a fact instead of supposing it. There the verb may go into the conditional or the future. "S'il ne viendrait pas volontiers, il viendra quand même" concedes reluctance rather than making it a condition.

Rare in speech, common in administrative writing, they stop you correcting a correct sentence.

What does the conditional do when there is no "si"?

This is where it becomes useful, and where courses stop too early. The office's page on the modal value of the conditional lists five uses, none of them with a visible "si".

Uncertainty, to report something without vouching for it. This is the journalistic conditional: "le bilan serait de trois blessés."
Politeness, softening a request, a piece of advice or an order: "je voudrais un café" rather than "je veux un café".
Concession, with the turn of phrase "ne savoir + infinitive".
Surprise or irritation, in an exclamation or a question: "moi, j'aurais dit ça ?"
Imagination, as in children's games: "moi je serais le capitaine."

English does the first with "reportedly", the second with "would like" and "could you"; French is more economical, one verb ending carrying both jobs. Politeness first, since it serves in a shop or an email from A2 onwards, then uncertainty, which is everywhere in the news.

What these rules do not tell you

First, institutions do not agree on what it is. The grammar terminology guide published by the French Ministry of Education rules that "le conditionnel, en dépit d'une tradition encore vivace, doit bien être considéré comme un temps de l'indicatif", the argument being the symmetry of chanterai, chanterais, chantai, chantais. Canada's Language Portal still titles its own page "conditionnel (mode du verbe)". If your textbook and your teacher classify it differently, neither is wrong.

Second, the rule describes the written standard, not all speech. Carmen LeBlanc analysed a corpus of French spoken in Canada's national capital region, 120 informants, in the Canadian Journal of Linguistics of July 2009: the conditional does appear inside "si" clauses, and the form of the verb there is determined by the modal reading of the utterance.

Three limits. The study covers one region of Canada and says nothing about the French of France or West Africa. It describes speech, not a model to imitate. And DELF and DALF examiners still mark against the school grammars, so keep the rule in writing.

What holds everywhere is the division of labour: "si" sets the scene, the conditional says what would follow. Good drill: take three memories and tell what would have happened otherwise. That is what an examiner listens for.

You can place your level with our level test, then drill these systems out loud with a qualified native teacher in a live class, one to one or in a small group of three to five students, with no subscription. Our articles on the subjunctive, on futur proche and futur simple and on passé composé and imparfait round this one out.