Understanding 'Si' Clauses in French

France, Paris, Young woman paying with her smartphone at parking automat
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Si clauses or conditionals produce conditional sentences, with one clause stating a condition or possibility and a second clause naming a result produced by that condition. In English, such sentences are called "if/then" constructions. The French si, of course, means "if" in English. There is no equivalent for "then" per se in French conditional sentences.

There are different types of si clauses, but they all have two things in common:

1) The English result clause might be preceded by "then," but there is no equivalent word preceding the French result clause.

   Si tu conduis, je paierai.
   
If you drive, (then) I'll pay.

2) The clauses can be in one of two orders: Either the si clause is followed by the result clause, or the result clause is followed by the si clause. Both work as long as the verb forms are paired correctly and si is placed in front of the condition.

   Je paierai si tu conduis.
   I'll pay if you drive.

Types of 'Si' Clauses

Si clauses are divided into types based on the likeliness of what is stated in the result clause: what does, will, would, or would have happened if.... The first verb form listed for each type names the condition upon which the result depends; the result is indicated by the second verb form.

  1. First conditional: Likely / Potentiel
    Present or present perfect + present, future or imperative
  2. Second conditional: Unlikely / Irréel du présent
    Imperfect + conditional
  1. Third conditional: Impossible / Irréel du passé
    Pluperfect + conditional perfect  

These verb pairings are very specific: for example, in the second conditional, you can only use the imperfect in the si clause and the conditional in the result clause. Memorizing these pairings is probably the most difficult part of si clauses.

It's important to memorize the rules concerning the sequence of tenses.

Please note that the term "conditional" here refers to the condition being named; it does not mean that the conditional mood is necessarily used in the conditional sentence. As shown above, the conditional mood is not used in the first conditional, and even in the second and third conditional, the conditional mood does not name the condition, but rather the result.

First Conditional

The first conditional* refers to an if-then clause that names a likely situation and the result dependent upon it: something that happens or will happen if something else happens. The term "conditional" here refers to the condition being named; it does not mean that the conditional mood is necessarily used in the conditional sentence. The conditional mood is not used in the first conditional.

The first conditional is formed with the present tense or present perfect in the si clause, and one of three verb forms—present, future, or imperative—in the result clause. 

Present + Present

This construction is used for things that happen regularly. Note that the si in these sentences could probably be replaced by quand (when) with little or no difference in meaning.

S'il pleut, nous ne sortons pas. / Nous ne sortons pas s'il pleut.
If it rains, we don't go out. / We don't go out if it rains.

Si je ne veux pas lire, je regarde la télé. / Je regarde la télé si je ne veux pas lire.
If I don't want to read, I watch TV. / I watch TV if I don't want to read.

Present + Future

The present + future construction is used for events that are likely to occur. The present tense follows si; it is the situation that is required before the other action will take place.

Si j'ai le temps, je le ferai. / Je le ferai si j'ai le temps..
If I have time, I will do it. / I will do it if I have time.

Si tu étudies, tu réussiras à l'examen. / Tu réussiras à l'examen si tu étudies.
If you study, you will pass the test. / You'll pass the test if you study.

Present + Imperative

This construction is used to give an order, assuming that the condition is met.

The present tense follows si; it is the situation that is required before the other action becomes a command.

Si tu peux, viens me voir. / Viens me voir si tu peux.
If you can, come see me. / Come see me if you can.
(If you can't, then don't worry about it.)

Si vous avez de l'argent, payez la facture. / Payez la facture si vous avez de l'argent.
If you have money, pay the bill. / Pay the bill if you have money.
(If you don't have any money, someone else will take care of it.)

'Passé composé' + Present, Future, or Imperative

Si clauses may also use the passé composé followed by the present, future, or imperative. These constructions are basically the same as above; the difference is that the condition is in the present perfect rather than the simple present.

Si tu as fini, tu peux partir. / Tu peux partir si tu as fini.
If you have finished, you can leave.

Si tu n'as pas fini, tu me le diras. / Tu me le diras si tu n'as pas fini.
If you haven't finished, [you will] tell me.

Si tu n'as pas fini, dis-le-moi. / Dis-le-moi si tu n'as pas fini.
If you haven't finished, tell me.

Second Conditional 

The second conditional* expresses something that is contrary to present fact or unlikely to occur: something that would happen, if something else happened. The term "conditional" here refers to the condition being named, not the conditional mood. In the second conditional, the conditional mood is not used to name the condition itself, but rather the result.

For the second conditional, use si + imperfect (stating the condition) + conditional (stating what would happen).

Si j'avais le temps, je le ferais. / Je le ferais si j'avais le temps.
If I had time, I would do it. / I would do it if I had time.
(Fact: I don't have time, but if I did [contrary to fact], I would do it.)

Si tu étudiais, tu réussirais à l'examen. / Tu réussirais à l'examen si tu étudiais.
If you studied, you would pass the test. / You would pass the test if you studied.
(Fact: You don't study, but if you did [unlikely to occur], you would pass the test.)

Si elle vous voyait, elle vous aiderait. / Elle vous aiderait si elle vous voyait.
If she saw you, she would help you. / She would help you if she saw you.
(Fact: She doesn't see you so she isn't helping you [but if you get her attention, she will].)

Third Conditional

The third conditional* is a conditional sentence that expresses a hypothetical situation that is contrary to past fact: something that would have happened if something else had happened.

Please note that the term "conditional" here refers to the condition being named, not the conditional mood. In the third conditional, the conditional mood is not used to name the condition itself, but rather the result.

To form the third conditional, use si + pluperfect (to explain what would have had to occur) + conditional perfect (what would have been possible).

Si j'avais eu le temps, je l'aurais fait. / Je l'aurais fait si j'avais eu le temps.
If I had had time, I would have done it. / I would have done it if I had had time.
(Fact: I didn't have time, so I didn't do it.)

Si tu avais étudié, tu aurais réussi à l'examen. / Tu aurais réussi à l'examen si tu avais étudié.
If you had studied, you would have passed the test. / You would have passed the test if you had studied.
(Fact: You didn't study, so you didn't pass the test.)

Si elle vous avait vu, elle vous aurait aidé. / Elle vous aurait aidé si elle vous avait vu.
If she had seen you, she would have helped you. / She would have helped you if she had seen you.
(Fact: She didn't see you, so she didn't help you.)

Literary Third Conditional

In literary or other very formal French, both verbs in the pluperfect + conditional perfect construction are replaced by the second form of the conditional perfect.

Si j'eusse eu le temps, je l'eusse fait. / Je l'eusse fait si j'eusse eu le temps
If I had had time, I would have done it.

Si vous eussiez étudié, vous eussiez réussi à l'examen. / Vous eussiez réussi à l'examen si vous eussiez étudié.
If you had studied, you would have passed the test.