¿Cómo determinar la diferencia entre: "si se puede" y "sí se puede"?

Question

On paper, it's easy to tell. But when speaking how do you determine the difference between si se puede and sí se puede?

I don't think context would always make it clear enough. Consider the question: "Hey, can I use your Legos to build a replica of the Death Star?"

Two possible answers:

Sí se puede.

"Sure, if you can..." Expressing uncertainty that accomplishing the task is possible.

Si se puede.

"Yes you can." Sure, go ahead and use them.

So, how does one tell the difference? In this case you still get permission either way, but I feel like this is a nuance that shouldn't be left unconsidered.

Answer 1

Note: sí = yes; si = if

Conditional sentences are made of two parts: a protasis (if-clause) and an apodosis (consequence).

Any conditional sentence requires both elements, although sometimes the apodosis is elided because it can be deduced from the context. However, if this is the case, the sentence is still incomplete for it's lacking the second part, and this incompleteness is expressed in speech trough intonation: generally (although not always), the tone will rise towards the end of the sentence. This happens especially if the speaker intends to say that he/she is somehow questioning the protasis is real or appropriate. See the example below:

A: ¿Puedo salir esta noche con mis amigos?

B: Si crees que has estudiado lo suficiente.

Here, if B (a mother) thinks A (her son) has not studied enough or that it isn't appropiate that he go out with his friends because he's taking an important exam the next day, she would imply such thing by rising her tone towards the end of the sentence. If that's not the case, and she's just saying her son is allowed to go out if he thinks he has studied enough, her tone wouldn't rise.

So to answer you question, if the speaker thinks you can't make a Death Star out of Legos, their tone would rise. If they are simply answering "sí se puede", their tone wouldn't.

But, what if they don't have any expectations as to whether you can or not? Then the difference between both sentences wouldn't be that clear. Nevertheless, whereas in negative sentences the "no" particle is strictly necessary, in affirmative sentences the "sí" particle is not so. If the speaker decides to make the "sí" explicit, they will emphasize it with their tone:

Pepe no va a ir a la fiesta, pero yo sí voy a ir.

That "sí" is stressed, and so would be the "sí" in "sí se puede". The "si" in "si se puede" would never be stressed. Therefore, it's unlikely to be any ambiguity.

Finally, even though "si se puede" (if you can) and "sí se puede" (indeed you can) are both perfectly grammatical, they don't sound too natural in this case because you don't generally use an impersonal tense to say "Yes, you can", but just "Sí, puedes".

Answer 2

The stress determines the difference.
sí se puede is the actual response for something that can actually be done. Often, short affirmative answers in Spanish put a comma after sí, so the actual answer is just sí, se puede.

But si se puede, stands for a condition.
si se puede needs a result clause in order to show to the speaker if he/she has the ability to perform it. For instance,

— Si se puede, hazlo.
— Si es que puedes, hazlo.
— Si es que se puede, hazlo.

After the comma we can add the adverb entonces to use it as a consequence if the first clause is triggered.

— Si se puede, entonces hazlo.
— Si es que puedes, entonces hazlo.
— Si es que se puede, entonces hazlo.

However, this response is normally given when the question is paraphrased as Oye, ¿se pueden usar legos para construir una réplica de la Estrella de la Muerte?
But in this case since we have legos, we use

— Si se pueden (usar), entonces hazlo.
— Si es que puedes (usarlos), entonces hazlo.
— Si es que se pueden (usar), entonces hazlo.

Answer 3

Considero que "si se puede" se establece para iniciar una condición y luego solicitar algo que se desea, por lo que debemos terminar la frase, por ejemplo, "si se puede, me gustaría conocer los detalles sobre ese retrato"

Por otra parte "sí se puede" creo que debería llevar una coma después de sí, quedaría así": "sí, se puede", lo utilizaríamos a modo de autorización, es decir, dar permiso para algo que se nos haya solicitado.