How to say "could" in spanish?
This has been driving me nuts lately, and I believe I know the answer, but I'm just clarifying.
I believe there are two definitions of "could" in English. 1) the past tense of "can" or "to be able to" (which are synonyms). 2) the conditional tense of "can" or "to be able to." If these are true, than you would simply use the past and conditional forms of "poder."
But my questions are: Am I correct? Are there any other definitions of "could" in English that are translated into Spanish a different way? And are there any other definitions of the past and conditional tenses of poder that are translated into something else in English other than "could," "was able to," or "would be able to"?
5 Answers
It looks like you've got the basics down, good job. 
I wouldn't focus so much on directly translating a conjugation and instead focus on how to say something using the Spanish-language mindset (ahum ahum grammatical system), but I understand why you think from your native language. Be careful: the English imperfect is something else entirely from the Spanish imperfecto!
Indeed in the most common case, 'could' means 'was or would be able to', which in Spanish is said with (was able to) the imperfecto (podía etc.) & pretérito (pude etc.) and (would be able to) condicional (podría etc.) and sometimes imperfecto del subjuntivo (pudiera etc.).
'Could you' is also used figuratively (+ formally) to mean 'are you willing to?' in f.e. 'Could you close the window, please?' you obviously don't ask after their ability, but it's translated all the same: 'Podría/Pudiera usted cerrar la ventana, por favor?".
Similarily, 'Could I' more often than not really asks for permission, meaning 'May I?' Spaniards agree however that this is a nice way to phrase it, and again use 'poder'.
Sometimes, natives of Spanish prefer to omit the word, though. For example:
Could I borrow your newspaper? -> ¿Me prestas el periódico? (literally: You lend me the newspaper?)
Also when we talk about the senses: seeing, hearing etc.:
I couldn't see her anywhere. -> No la veía en ninguna parte.
Of course, Spanish doesn't have the same set expressions as English..:
I could have hit him! (on purpose) -> ¡Me dieron ganas de pegarle! (literally: he gave me the urge to hit him!)
they couldn't help it --> ellos no tienen la culpa (literally: they didn't have the fault)
the dog was as happy as could be when his master returned -> el perro estaba de lo más feliz cuando volvía su maestro (literally: he was of the most happy)
In many more cases than you'd think, though, Spanish does use 'poder' where in an English expression you see 'can'.
However, when 'could' refers to 'knew how to' (skills), Spanish tends to use 'saber' (to know) instead:
he couldn't swim -> no sabía nadar (if he knew how to, but he'd have had his legs broken, you'd use poder)
Click here for an explanation of all 11 English Modals and sentence examples in Spanish and English.
I posted this thread on the 6th Dec 2012.
Here is a little more information of the "modal verb" could:
When the word “could” is used it usually does not mean the past tense of “can”. It usually means “There is a possibility that”. For example: “I could help you with that” means “There is a possibility that I will help you with that”. The phrase “could have” used with the past participle of the verb expresses the past tense of “can”, but it also means that the action did not take place: She could have driven you to the store (but she did not).
You have to be careful translating from English to Spanish with this and all modal verbs. Some times you need the conditional tense in Spanish and sometimes you need the subjunctive mood. Si pudiera ayadarte lo haría. Is how I would (another modal) say If I could help you I would. I don't know if that is good Spanish as I am not a native speaker. Someone will correct it if it isn't.
Modals don't exist in Spanish so direct translations are not possible.
Could is not the passed tense of anything.
Can is not the same as "to be able to" = "poder" - poder is a verb - can is not.
I can do it now. - present ability = I am able to do it now and I might do it.
I could do it now. - present possibility = I am able to do it and there is a possibilty I will.
I could do it yesterday. - past possibilty = I was able to do it and there is a possibilty I did.
I could do it tomorrow. - future possibility = I will be able to do it and there is a possibilty I will.
This will help with modals note: In my opinion Modals are NOT verbs.
There are all sorts of "could" in English, and you'd be surprised how they turn out in Spanish.
There is the "could" which is the past tense of "can" or "to be able"
It was the one thing I could do. "Fue la única cosa que podía hacer" That's "poder" in the imperfect.
I hope this will start your off. "Poder" can be be used in "any" tense or mood. Spanish has four moods, but I will not confuse you with them at this time.
Here's one from the "imperfect subjunctive"
"¡Ojalá que pudiera hablar mejor el español! "Oh how I wish I could speak Spanish better! If you know little about the subjunctive, this might not help you.
Does that clear up the mud somewhat? Let me know please by commenting under this post.
