Odd si clause

From L11.5

Vous pourrez partir, si vous avez fini vos devoirs.

(You will be able to leave, if you have finished your homework.)

This strikes me as very peculiar. It seems that this would normally be phrased as either, You will be able to leave, when you have finished your homework; or You are able to leave if you have finished your homework.

Here's the rub. In the original sentence, although it's referring to being able to leave in the future, it's ruling out the possibility that you still have time to finish your homework.

So, in trying to come up with a si clause that includes passé composé and future tense that didn't seem peculiar, I came to the conclusion that you would only use this particular construction if it was the case that you were referring to a future event and something that, if it happened, had to have already happened. For example:

The good seats are all sold out. You  will sit up front, (only) if  you have (already) purchased your ticket.

And yes,  passé composé means it already happened, but as I see it, in order for the construction to be appropriate, it needs to be ruling out the possibility of the condition also being met at some other point in time prior to the future event.

Is this conclusion correct?

If this is the case, I think knowing when one might use a particular construction is just as important as knowing that it exists. (And I think the ex. in the lesson is a weak one.)

Robert

Bonjour Robert, 

Sorry for the late reply. 

I would be inclined to say: 

• Vous pourrez partir, dès que vous avez fini vos devoirs. (You'll be able to leave, as soon as you have finished your homework.) 

I understand this is a completely different conjunction, but I wanted to provide the example to illustrate the fact that si is working a bit like dès que and that you are likely to hear this when speaking with native speakers. I realise this doesn't help someone wanting to learn the language meticulously,  however grammatical laziness exists in native speakers of all languages, everywhere. 

I also want to present different possible translations of the example because there are three possible equivalents of the passé composé in English and in seeing all three, it bolsters the point you are making. 

Vous pourrez partir, si vous avez fini vos devoirs. 

1. You will be able to leave, if you finished your homework. - simple past 
2. You will be able to leave, if you have finished your homework. - present perfect 
3. You will be able to leave, if you did finish your homework. - past emphatic 

They all sound quite cumbersome to me and would require some specific contexts or more information for them to work. I'm thinking something like, “If you finished your homework (yesterday), you will be able to leave (on time, otherwise you will have to stay after class until it's completed)." or "You will be able to leave (early), if you have finished your homework (from yesterday, otherwise you will have to stay until it is done).” 

You are correct in your conclusion and the example you pulled simply doesn't have enough context baked into it for it to work well.  

I hope this helps, 

   -   Mitchell

Ok, we seem to have arrived at the same conclusion. And, yes, I get your point about strict interpretation of the meaning is going to be difficult when the speaker may not have intended strict interpretation.

So, here's my conclusion. In order for the passé composé and future tense si clause to be meaningful and not awkwardly contrived, the following conditions must be met.

The event that would satisfy the condition must have already taken place, not just because it's past tense, but because the situation that's being referred to requires that this is not optional. In other words, there must be a meaningful and necessary time gap between the events. And also, the speaker, for whatever reason, must not know what the outcome of the prior event was at the time the sentence was formed, even though one might expect it to be already known, since it already happened.

Examples:

You will have tomatoes next month if you have (already) planted seedlings in April.

I will start dinner now if you (already) brought everything I need with you.

This framing will support the roof if the foundation was (already) properly constructed.

Thanks for your time, Mitchell.

Robert

Bonjour Robert,

No problem, I think we are on the same wave length. 

Sorry the example wasn't fully up to scratch, but thanks for bringing it up; for me it was a good discussion top and for others it serves as a good reference should anyone run into the same issue.

   -   Mitchell