The real conditional
A conditional sentence has two halves: the condition introduced by si, and the result in the main clause. In this first type the condition is realistic – it genuinely may happen, and if it does, the result follows.
This is the first conditional you know from English: if it rains, I'll stay home. The si-clause is in the present, even when the event lies in the future – English refuses will there too. If the condition is already fulfilled, French uses the passé composé: Si tu as fini, tu peux partir. The main clause chooses between present, future and imperative.
The three combinations
Only the left half is fixed: si + present. What the main clause takes depends on whether you are stating a rule, predicting one future event, or giving an instruction.
Present - what is always true
For habits, rules, laws of nature and anything that happens the same way every time. Both halves stay in the present.
Si on chauffe l'eau à cent degrés, elle bout.
If you heat water to a hundred degrees, it boils.
Si je bois du café le soir, je ne dors pas.
If I drink coffee in the evening, I don't sleep.
S'il pleut, le match est annulé.
If it rains, the match is called off.
Futur simple - one event ahead of us
For a specific event still to come, the main clause is in the future. The si-clause stays in the present: after si (= if) there is never a future and never a conditional. Only where si means whether is the future normal: Je ne sais pas s'il viendra (I don't know whether he will come).
Si j'ai le temps, je viendrai demain.
If I have time, I'll come tomorrow.
Si tu travailles bien, tu réussiras.
If you work hard, you'll succeed.
Si nous partons maintenant, nous arriverons à l'heure.
If we leave now, we'll arrive on time.
Imperative - advice and instructions
Instead of a result, the main clause can carry an instruction, as in advice, safety notices and user manuals.
S'il pleut, prends un parapluie.
If it rains, take an umbrella.
Si tu ne comprends pas, demande-moi.
If you don't understand, ask me.
Si vous avez un problème, appelez ce numéro.
If you have a problem, call this number.
Order and word order
The si-clause can come first or last without changing the meaning. First, and a comma separates the halves; last, and the comma usually disappears – exactly as in English. The main clause keeps its normal word order: S'il pleut, je reste à la maison.
Si tu veux, on peut y aller ensemble.
If you like, we can go together.
On peut y aller ensemble si tu veux.
We can go together if you like.
si or quand?
Si means if: it may or may not happen. Quand means when: it certainly will, only the timing is open. So far, so English. The twist is the tense that follows.
si - if, it might happen
Followed by the present, just like English.
S'il pleut, on ne sortira pas.
If it rains, we won't go out.
Si Paul arrive, préviens-moi.
If Paul arrives, let me know.
quand - when, it will happen
For a future event, followed by the future – and this is where English and French part company. English says when summer comes; French says quand l'été arrivera.
Quand l'été arrivera, on ira à la mer.
When summer comes, we'll go to the seaside.
Quand je finirai le travail, je t'appellerai.
When I finish work, I'll call you.
Keep the pair in your head as one item: si tu viens against quand tu viendras.
