Modal: Could

Could is the past tense of can, but it carries a second, equally important identity: it is also the subjunctive, hypothetical form of can — the version that steps back from certainty and opens the door to politeness, uncertainty, and imagined possibilities.

As a past-tense modal, could describes general past ability: When I was younger, I could run for ten miles. But crucially, could does not describe a single successful past action. You cannot say I could pass the exam yesterday to mean you passed it — for that, use I was able to pass or I managed to pass. Keep that distinction: general past ability = could, one-off past achievement = was able to.

Beyond the past, could is the go-to modal for polite requests. Could you help me with this? is softer and more deferential than Can you help me? Compare the ladder of request politeness: Will you? (most direct) → Can you? → Could you? → Would you? (most polite). Could sits near the polite end of that scale.

Could also expresses possibility — not in the past, but in the present or future. It could rain later means rain is a real possibility, though not certain. Compared with may (more formal possibility) and might (lower certainty), could occupies the middle ground of everyday speculation. In second conditional sentences, could replaces can in hypothetical worlds: If I had more time, I could learn the guitar.

The subjunctive nature of could also powers emotional uses. I wish I could fly expresses an unreal desire. You could at least have called! uses could for angry emphasis. And in suggestions — You could try restarting the computer — could offers an idea without imposing it, giving the listener full freedom to accept or ignore. Where can asserts and would imagines, could drapes possibility over past, present, and hypothetical alike.