Hi Janet,

If you use “compras” I'm fairly sure that it will change the emphasis of the sentence. In the lesson, they give an alternative structure, with an example of a sentence which uses the present indicative both immediately after cuando, and in the second part of the sentence; “Cuando voy de vacaciones a Tenerife, me hospedo en el hotel Olimpia.” When I go to Tenerife I stay in the hotel Olimpia - [not I will stay].

So there is no subjunctive conjugation after cuando, and there is a present form of hospedarse rather than a future in the second half of the sentence. This is because the speaker wants you to know that he or she is talking about something they do whenever they travel there, rather than saying what they are going to do the next time they travel. It is a subtle difference but clearly two possibilities.  

I think - and I would really like the teachers to confirm this - if you change the conjugation to "compras" which means “you buy,” the meaning changes because it is no longer the imperative “buy!!!!” nor is it about a future event still to happen, but rather is something that happens (normally) whenever you go to the market. Here is an example which I hope is correct. Imagine a friendly conversation where someone is saying “When you go to the market, you buy fruit [don’t you]?” “Cuando vas al mercado, compras fruta ¿no?” 

In this context there is no imperative, and hence no future, and no need for the subjunctive, and the meaning relates to something that happens all the time / normally. So I don't think you can keep the subjunctive after cuando and have a present conjugation in the second part of the sentence. The teachers may of course have exceptions to the rule.

Saludos. John

Thanks, John, but I'm still confused. Isn't the imperative in the present (El presente refers to the present time. Spanish present tense is included under the moods indicativo and subjuntivo) since it uses the present to conjugate the subjunctive? I don't see the difference in timing or meaning with "Buy fruit!" vs "Buy fruit". 

Hi Janet,

Yes the imperative is definitely in the present tense. The subjunctive is used where the outcome is not known or there is doubt; among other uses. Hence this lesson is pointing out the use of Cuando + the subjunctive for those times when the outcome is not known, and they are saying that the subjunctive conjugation follows immediately after "Cuando" in cases where this doubt exists. 

This is suggesting that only two options are then possible. 1. The second part of the sentence must have either the imperative / an instruction, OR a future intention). 

This is what I meant by having the present indicative would change the nature of the sentence. If it were to take a conjugation in the present like "compras", you would have a sentence like "When you go to the market you buy fruit and vegetables." This is a perfectly good sentence but the outcome is known - there is no doubt. Hence the subjunctive becomes redundant, and you would have to have present indicative both after cuando and in the second part of the sentence. It is like a statement of what person 1 says that person 2 does when he or she goes to the market. It is their routine, hence no doubt.

There are often exceptions in Spanish and it could mean that the structure you suggested can be used in certain situations. I was hoping that the teachers would join in and let us know.

All the best

John

Hi Janet, I've been learning that the tense is not always the same as the time frame.  (For example, there is even a construction in which we use the present tense to talk about the past, if we are describing something that almost happened).

So a tense such as the imperative can be used to refer to the future time frame, since tense does not equal time frame.