Question: It sometimes seems there’s no difference between can and could. Is there?

Grammar: Modal Verbs

In requests, both are correct and have the same meaning. Could is used for more formal or polite situations.

Could you send me an application form? (formal)

Can I borrow your pen? (informal) In talking about abilities and skills, could indicates past tense:

I can play the piano.

I could play the piano when I was only three.

When talking about availability in the negative, we can also use could.

I’m sorry that I couldn’t come to your party last night.

However, in the positive, we use ‘able to’ for this purpose:

I finished my homework early, so I was able to go to the party.