French learners write si j'aurais because English says if I would. It is a classic slip in si clauses in French, and the rule that prevents it is short: after si meaning if, never the conditional and never the future.

Here are the three patterns, the mixed case that is allowed, and the one situation where si can take the future after all.

1. Si clauses in French: the rule first

When si introduces a condition, the verb right after it is in the present, the imparfait or the plus-que-parfait. The future and the conditional go in the other half of the sentence, never after si.

• Si j'avais le temps, je viendrais. Not si j'aurais le temps.
• S'il pleut demain, on restera ici. Not s'il pleuvra.

2. The three si clause patterns

Each pattern pairs a tense after si with a tense in the main clause.

After si	Main clause	Meaning	Example
present	future, present or imperative	a real possibility	Si tu viens, je cuisinerai.
imparfait	present conditional	imagined now	Si j'avais une voiture, je partirais.
plus-que-parfait	past conditional	a past that did not happen	Si j'avais su, je serais venu.

The conditional itself, and how it differs from the future, is covered in future or conditional.

3. Si + present: real possibilities

Use the present after si for things that may really happen. The main clause takes the future, the present for general truths, or the imperative for advice.

• Si tu finis tôt, on ira au cinéma.
• Si on chauffe l'eau à 100 degrés, elle bout.
• Si tu as froid, prends mon pull.

4. Si + imparfait and si j'avais: the imagined present

The imparfait after si describes a situation that is not real now: si j'avais, si j'étais, si nous pouvions. The main clause takes the present conditional.

• Si j'étais toi, j'accepterais.
• Si nous habitions plus près, nous viendrions plus souvent.

The imparfait here does not describe the past at all, which is why it surprises learners who know it from imparfait or passé composé.

5. Si + plus-que-parfait, and mixing the patterns

For a past that did not happen, use the plus-que-parfait after si and the past conditional in the main clause: si tu m'avais prévenu, je serais venu.

The patterns can mix when the consequence is in the present: si j'avais pris ce train, je serais déjà à Paris (past condition, present consequence). The rule still holds: no conditional after si.

Wrong	Right	Why
Si j'aurais su	Si j'avais su	no conditional after si
Si je serai libre	Si je suis libre	no future after si
Si il vient	S'il vient	si becomes s' before il and ils
Si elle viendrait	Si elle venait	imparfait after si

6. When si means whether

The rule applies to si meaning if. When si means whether, in an indirect question, the future and the conditional are allowed: je me demande s'il viendra, elle ne savait pas s'il viendrait. Test: if you can say whether in English, any tense can follow.

Si also elides before il and ils (s'il, s'ils) but never before elle or on, a point covered in the apostrophe in French.

The habit to keep

Look at the verb right after si. If si means if, that verb is in the present, the imparfait or the plus-que-parfait, never the conditional. Apostrophe· dictates full si sentences and shows the rule whenever the tense slips.

Frequently asked questions

Can you use the conditional after si in French?

Not when si means if: si j'avais, never si j'aurais. The conditional goes in the other clause. When si means whether, as in je me demande s'il viendrait, it is allowed.

What tense follows si + imparfait?

The present conditional: si j'avais le temps, je voyagerais. The pair describes something imagined in the present.

Is it si j'aurais or si j'avais?

Si j'avais. After si meaning if, French uses the imparfait, never the conditional, even though English often says if I would.

How do French conditional sentences work with si + present?

With si + present the condition can really happen, and the main clause is in the future, the present or the imperative: si tu viens, je cuisinerai.

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