Спасибо! Значит, could чаще имеет оттенок со смыслом "бы".
Но вот примеры из уроков Puzzle English.
I could swim before I could walk. Я мог плавать раньше, чем ходить.
You could play the piano. Ты умел играть на пианино.
... и добавил:
Выходит, тупо прошедшее время от "can", безо всяких "гипотетических возможностей" — абсолютно законный вариант употребления этого словечка.
а еще есть "Would," and "Should" и сколько по работе общаюсь с буржуями, никто особо в разговоре не обращает внимание на эти формы - что сказал, то сказал.
Чего не скажешь про употребление этих форма в письме или в текстах каких-нибудь мануалов (инструкций). Там все четко.
Could is used to say that an action or event is possible.
Would is used to talk about a possible or imagined situation, and is often used when that possible situation is not going to happen.
Should is used to say that something is the proper or best thing to do, or to say that someone ought to do something or must do something.
-Adam could visit us on Monday. This tells us that it is possible Adam will visit on Monday, maybe he can visit us, but maybe he has other options, too. Visiting us is one possibility.
-Adam would visit us on Monday. This tells us that we can imagine a situation in which Adam wants to visit us on Monday, but maybe it is not actually possible. Adam is willing to visit us, under the right conditions or if he can.
-Adam should visit us on Monday. This tells us that Adam visiting on Monday is a good idea, or that it is something Adam is obligated to do.