What are the three types of si clause in French?

Type 1, the real and likely case: si + present in the if-clause, then present, future or imperative in the main clause - si tu veux, je viens; s'il pleut, je resterai. Type 2, the hypothetical or unreal present: si + imperfect, then the present conditional - si j'avais le temps, je viendrais (if I had time, I would come). Type 3, the unreal past for regret: si + pluperfect, then the past conditional - si j'avais su, je serais venu (if I had known, I would have come). Each type is a fixed tense pairing; learn the pairs and the sentences build themselves.

Can you use the future or the conditional after si in French?

No - this is the golden rule of si clauses. After a conditional si you never use the future (not 'si je serai') and never use the conditional (not 'si j'aurais'). The verb after si is always the lower tense of the pair: present, imperfect or pluperfect. The future and conditional live in the main clause, not the if-clause. The one apparent exception is si meaning 'whether', which is a different word entirely and does allow the future: je ne sais pas si elle viendra (I do not know whether she will come).

When does si become s' in French?

Si elides to s' only before il and ils - so s'il pleut (if it rains) and s'ils viennent (if they come). It never elides before anything else: it stays si elle, si on, si un, si une and, crucially, si j'avais (the i of si does not drop before je). So you write s'il but si elle, and si j'avais su, never 's'j'avais'.

French si Clauses

A si clause is an "if" sentence: a condition, and a consequence that depends on it. French handles them with a tidy three-type system, and the whole thing rests on one principle - the tenses come in fixed pairs. Choose the type, and both halves of the sentence are decided for you.

The three types map onto how likely or how real the condition is: a real possibility, a hypothetical present, and an impossible past. Learn the three pairings and you will never have to guess.

The three types at a glance

Type	If-clause (after si)	Main clause	Meaning
1	present	present / future / imperative	real, likely
2	imperfect	present conditional	hypothetical present
3	pluperfect	past conditional	unreal past (regret)

Notice the pattern down the if-clause column: present, imperfect, pluperfect. Each step takes the condition one notch further from reality. And notice that the if-clause never contains a future or a conditional - that is the golden rule, and we come back to it below.

Type 1: real and likely (si + present)

Use Type 1 when the condition is a genuine possibility. The if-clause is in the present, and the main clause is in the present, the future, or the imperative.

Si tu veux, je viens. (If you want, I will come.) - present + present.
S'il pleut, je resterai a la maison. (If it rains, I will stay at home.) - present + future.
Si tu as faim, mange quelque chose. (If you are hungry, eat something.) - present + imperative.
Si vous finissez tot, vous pourrez sortir. (If you finish early, you will be able to go out.) - present + future.

The future-in-the-main-clause version is the everyday workhorse: a real condition now, a likely result later. The verb after si stays in the present even though English often slips in a "will" - "if it rains", not "if it will rain".

Type 2: hypothetical present (si + imperfect)

Use Type 2 for things that are not actually the case - imaginary, contrary-to-fact situations in the present. The if-clause goes in the imperfect, and the main clause in the present conditional.

Si j'avais le temps, je viendrais. (If I had time, I would come.) - but I do not have time.
Si tu etais riche, qu'est-ce que tu ferais? (If you were rich, what would you do?)
Si on partait maintenant, on arriverait a l'heure. (If we left now, we would arrive on time.)
Si elle parlait italien, elle travaillerait en Italie. (If she spoke Italian, she would work in Italy.)

This is the English "if I had... I would..." pattern exactly. The condition is unreal, so French steps it back into the imperfect, and the consequence sits in the conditionnel. The formation of the conditional is covered in full on its own page; here, all that matters is the pairing - imperfect after si, conditional in the result.

Type 3: unreal past, the language of regret (si + pluperfect)

Use Type 3 for the impossible past - what would have happened if things had been different. It is the tense of regret and reproach. The if-clause goes in the plus-que-parfait, and the main clause in the past conditional (the conditional of avoir or etre + past participle).

Si j'avais su, je serais venu. (If I had known, I would have come.)
Si tu m'avais ecoute, tu n'aurais pas fait cette erreur. (If you had listened to me, you would not have made that mistake.)
Si nous etions partis plus tot, nous aurions evite les embouteillages. (If we had left earlier, we would have avoided the traffic.)
Si elle avait revise, elle aurait reussi l'examen. (If she had revised, she would have passed the exam.)

Si j'avais su (if I had known) is worth memorising whole - it is the standard French for "had I known". The pluperfect after si is built and explained on the plus-que-parfait page.

The golden rule: never future or conditional after si

This is the single most important point on the page. After a conditional si, you never use the future and you never use the conditional. The verb directly after si is always the lower tense of the pair - present, imperfect or pluperfect.

Wrong: ~~si je serai~~ -> Right: si je suis (Type 1).
Wrong: ~~si j'aurais~~ -> Right: si j'avais (Type 2).
Wrong: ~~si j'aurais su~~ -> Right: si j'avais su (Type 3).

A quick mental check: the future and the conditional belong in the main clause, not in the if-clause. If you find yourself writing a "-rai" or a "-rais" ending straight after si, stop - it is almost certainly wrong. The result clause carries the future/conditional; the si clause carries the plainer tense.

si meaning "whether": a different word

There is one place where a future or conditional can follow si, and it catches people out. When si means "whether" (introducing an indirect question), it is not a conditional si at all, and the normal tense rules apply - including the future and the conditional.

Je ne sais pas si elle viendra. (I do not know whether she will come.) - future allowed, because this is "whether", not "if".
Il m'a demande si je viendrais. (He asked me whether I would come.) - conditional allowed, same reason.
Elle se demande si nous aurons le temps. (She wonders whether we will have time.)

The test: can you swap "if" for "whether" in the English without changing the meaning? If yes, it is the "whether" si, and the future or conditional is fine. If no - if it sets up a genuine condition - it is a conditional si, and the golden rule applies.

The elision: si becomes s' before il and ils only

Si elides to s' only before il and ils:

S'il pleut... (If it rains...)
S'ils viennent... (If they come...)

It does not elide before anything else, including other words that start with a vowel:

si elle (not "s'elle"), si on, si un, si une.
And it does not drop before je: it is si j'avais su, never "s'j'avais su" - the j' here is the elision of je, while si stays intact.

So the only two elided forms you will ever write are s'il and s'ils.

Worked examples

Si tu as le temps, appelle-moi. (If you have time, call me.) - Type 1, present + imperative.
S'il fait beau demain, nous irons a la plage. (If it is sunny tomorrow, we will go to the beach.) - Type 1, present + future.
Si je gagnais au loto, j'acheterais une maison. (If I won the lottery, I would buy a house.) - Type 2, imperfect + conditional.
Si tu etais la, tout serait plus facile. (If you were here, everything would be easier.) - Type 2.
Si j'avais su, je serais reste chez moi. (If I had known, I would have stayed home.) - Type 3, pluperfect + past conditional.
Si nous avions reserve, nous n'aurions pas attendu. (If we had booked, we would not have waited.) - Type 3.
Je ne sais pas si tu auras le temps. (I do not know whether you will have time.) - "whether" si, future allowed.

Common mistakes English speakers make

The headline error is breaking the golden rule - putting a future or a conditional after si. English "if I will have time" tempts learners into "si j'aurai le temps", but it must be si j'ai le temps; and the regret form is si j'avais su, never "si j'aurais su". The second trap is mixing the pairs across types: a Type 2 if-clause needs the imperfect, so it is si j'avais le temps, je viendrais, not "si j'ai le temps, je viendrais" when the meaning is hypothetical. The third is mishandling the "whether" si - learners over-apply the golden rule and write "je ne sais pas si elle vient" when they mean the future, but je ne sais pas si elle viendra is correct because this si means "whether". Finally, watch the elision: it is s'il and s'ils only, so si elle, si on and si j'avais keep the full si.