Lesson 37: The full system of conditional sentences with si

Part 1: The one rule that changes everything

French si-sentences are structured. English speakers walk in with three bad habits from their own language: putting would after if ("if I would have known…"), or putting will after if ("if you will come…"), or reaching for a subjunctive. In French, drop all three instincts. Si is allergic to conditionnel, futur, and subjonctif.

French gives you three and only three sanctioned combinations. Learn them like a multiplication table.

Burn this into your memory:

After si, never use futur and never use conditionnel. This is the single most common English-speaker mistake. Si je serai… — wrong. Si je serais… — doubly wrong. Si je serais venu… — that's the English "if I would have come" sneaking in. French says si j'étais venu.

The conditional/future lives in the other clause. Si protects its own clause from any "would" or "will" tense.

Word order

The two halves are reversible — the meaning doesn't change. You only need a comma when si comes first:

• Si tu viens, je serai content. = Je serai content si tu viens.

Part 2: Type I — Real condition

Formula: si + présent → présent / futur simple / impératif

Used when the condition is realistic — it might actually happen, and you're predicting the consequence.

Trap #1 — the English "if … will" reflex. In English you can say "If you will come tomorrow, I'll be glad" — which is the most natural reading of a future condition. In French, the future lives only in the right half. Si tu viendras demain — wrong. It must be: Si tu viens demain, je serai content. Use the present tense inside si; let futur sit in the main clause.

Mini-shortcut. English "if X, will Y" maps cleanly onto French si + présent, futur. The only adjustment your brain has to make: kill the future tense inside the si-clause and replace it with the present.

Part 3: Type II — Hypothetical condition

Formula: si + imparfait → conditionnel présent

Used when the condition is unreal now or unlikely: fantasy, daydream, polite hypothetical.

English maps perfectly here. "If X, would Y" → Si + imparfait, conditionnel. Compare: "If I were rich, I would buy a house" → Si j'étais riche, j'achèterais une maison. The English "were" (subjunctive remnant) corresponds exactly to the French imparfait. The English "would buy" matches the French conditionnel.

Trap #2 — the English "would" leak. English speakers want to say "If I would have money…" or "If I would be rich…". In French this is a flat-out error. No conditional after si. Si j'aurais — Si je serais — both wrong. Use imparfait: Si j'avais — Si j'étais.

Reminder from Lesson 28: Conditionnel présent

Formula. Take the futur simple stem and stick on imparfait endings: -ais, -ais, -ait, -ions, -iez, -aient.

avoir → j'aurais, tu aurais, il aurait, nous aurions, vous auriez, ils auraient être → je serais, tu serais, il serait, nous serions, vous seriez, ils seraient faire → je ferais | aller → j'irais | venir → je viendrais | pouvoir → je pourrais

Part 4: Type III — Counterfactual past

Formula: si + plus-que-parfait → conditionnel passé

Used to say: "in the past, things were otherwise — but it didn't happen". Regret, reproach, alternative history. This is the "if I had known, I would have…" tense pair.

Trap #3 — the killer English mistake. English says "If I would have known, I would have come." That double would have is wrong in English textbooks and catastrophically wrong in French. The first would have must be turned into "had": "If I had known…" → Si j'avais su. Pattern: English "If had X, would have Y" → French si + plus-que-parfait, conditionnel passé. Both halves stay locked in their own tense.

Reminder from Lessons 26 and 29: building the tenses

Plus-que-parfait (L26). Imparfait of avoir/être + past participle: j'avais fait, j'étais allé(e).

Conditionnel passé (L29). Conditionnel présent of avoir/être + past participle: j'aurais fait, je serais allé(e).

Participle agreement works exactly as in passé composé: with être — agree with the subject; with avoir — agree with the direct object only if it sits to the left.

Part 5: Mixed conditionals

Life is messier than three types. You can splice a past condition with a present result, or the reverse.

Note. Mixed conditionals aren't a fourth type — they're just logic. If the cause is in the past but the consequence is today, combine accordingly. The left-side bans still apply: no futur, no conditionnel after si. Ever.

Part 6: Alternatives to si (same logic, different connector)

Crucial contrast. Si takes the indicative (présent, imparfait, plus-que-parfait). À condition que, pourvu que, à moins que take the subjunctive. Don't mix them up: Si and the subjunctive are not friends.

English heads-up. au cas où (literally "in the case where") is one of the few French conjunctions that actually does take conditionnel. It's not a contradiction of the si rule — au cas où is a different conjunction with its own grammar. Don't try to import the rule into a si-clause.

Part 7: Wishes and regrets — si seulement and si with no main clause

To express a pure wish or regret, French uses si without a main clause.

• Si seulement j'avais plus de temps ! — If only I had more time!
• Si seulement tu avais écouté ! — If only you had listened!
• Et si on allait au cinéma ? — What if we went to the movies?

English parallel. "If only" + past tense in English is exactly the French pattern. "If only I had more time" = imparfait. "If only you had listened" = plus-que-parfait. Pure structural equivalence — no surprises.