Can and could with the future



I was teaching modals recently and I noticed that can and could can both be used for the future:

I can go tomorrow.
I could go tomorrow.

Are there some instances in which these have the same meaning?




There are instances in which could can refer to the future and has the same meaning as can:

1. As a polite request:


Can/Could you help me, please?

2. As a suggestion:


There are other ways to get there. You don't have to cross the bridge. You can/could take the ferry, or you can/ could drive around the whole bay.

In sentences (a) and (b) above, either can or could may be used.

3. As part of a conditional sentence, the meaning is different with could:


Well, I could go with you.

A complete sentence might be:


Well, I could go with you if you really wanted me to.

In sentences (c) and (d), changing could to can alters the meaning of the sentence; you would have to alter the if-clause, too:


Well, I can go with you if you really want me to.

The sentences in (3)—sentences (c), (d), and (e)—do refer to the future, but can and could are not interchangeable here.



As Rachel notes, can and could have the same meaning in polite questions, with could being considered the more polite and more formal:

(a) Can you please open the door for me?


Could you please open the door for me?

They also have a very close meaning in the negative:

(c) That can't be true!


That couldn't be true!

(e) She can't have meant to insult you.


She couldn't have meant to insult you.

In reported speech, there's no real difference in meaning; the difference lies in immediate vs. later reporting of what was said and in the level of formality the speaker chooses, with the past form being the more formal.

(g) He said he can help us tomorrow. (immediate or informal reporting)


He said he could help us tomorrow. (later or more formal reporting)

To express possibility, could usually carries with it the idea of an implied condition. Using Rachel's example:

(i) You could take the ferry (if you wanted to, if that seemed like a good idea to you).


You can take the ferry. (a factual option)

Explaining to a non-native speaker the difference between sentences (i) and (j) would be no easy task! I've found that we can't and indeed shouldn't try to explain to students too finely nuanced differences in modal usage—but perhaps others have a different teaching experience?

While it's true that all modals are complicated, with varied usages and lots of nuances, it seems to me that could might possibly be the most complicated of all in terms of its many meanings and uses.

For me, the best sources on the meanings and uses of modals are dictionaries. The Collins COBUILD English Language Dictionary is a good source for teachers and researchers. For students, the Collins COBUILD English Dictionary for Advanced Learners is quite complete, and the Longman Advanced American Dictionary and Oxford Advanced Learner's Dictionary are quite accessible and useful for students' purposes.

Betty Azar

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