example sentence for conjugating poder

Question

Vosotras podéiscomprar lo que queráis. This is translated as: You can buy what you want.

I understand except for the last word "queráis ". I was expecting to see " queréis " for the "you want" at the end.

Looking up queráis, I see that it is the present subjunctive and have read that it is used if there is a change in the subject.

I can't see a change in subject. The first part of the sentence has "you" as subject ans so does the second part.

I expect that I've missed something crucial here so please help me to understand.

Thanks.

Accepted Answer

Hola Angela
As you said, "queráis" is the vosotros form of querer in the present subjunctive. The trigger for the subjunctive is not just limited to a change of subject in the main and subordinate clauses. In this case, the use of the present subjuntive is because of that nuance of "whatever you [may] want" as in the speaker doesn't know what they want to buy, he/she is not identifying in their head what they want. So this expresses uncertainty. 
Vosotros podéis comprar lo que queráis. [whatever those things might be]
It's also correct to use the present indicative here if the speaker knew what they wanted to buy; say for example, they'd had a conversation prior to this and they mentioned what items they are intending to buy: 
Vosotros podéis comprar lo que queréis. [those things you mentioned before]
I hope this clarified it.
Saludos cordiales
Inma