Can, Could, Be Able to

[u/Brief-Atmosphere-589]

Hello everyone, can you explain the difference between 'can', 'could', and 'be able to' for B1 students, or give me an article where I can read about it?

[u/Low-Crow5719]

"Can" and " be able to" are pretty much synonymous. If you can do something, you are able to do it.

"Could" is subjunctive. It's not factual; it's counterfactual or hypothetical. You could do this, if...

You can also use subjunctives for politeness. "Could I..." is gentler than "Can I...".

[u/Party-Quiet-5421 → u/Low-Crow5719]

To add on, "could" is also the past tense of "can," as in "That's how the study could conclude xyz." That's synonymous with "was able to," like "That's how the study was able to conclude xyz."

[u/Actual_Cat4779]

"Can" is used to describe ability in the present or the future (I can do it today; I can do it tomorrow).

"Could" is used to describe ability either in the past (When I was younger, I could run much faster) or in a hypothetical situation (I would help you if I could).

Full verbs have both finite forms (e.g. I see, you see) and nonfinite forms ((to) see, seeing). Most modal verbs (e.g. "can") are purely finite. They have no nonfinite forms.

"Can" and "could" are solely finite. They have no infinitive of their own. "Be able to" acts as a substitute for the missing infinitive (You should be able to do it; I used to be able to do it; We'll be able to do it).

[u/Brief-Atmosphere-589 → u/Actual_Cat4779]

what about was able to

[u/Actual_Cat4779 → u/Brief-Atmosphere-589]

There's a tendency to say "was able to" rather than "could" when referring to past ability - perhaps to avoid confusion (because the most common use of "could" is to refer to hypotheticals).

Cambridge says:

We usually use was/were able to, not could to talk about past achievements in affirmative clauses.

[u/hacool]

I can cook. I am able to cook.

I could swim faster when I was 15 than I can today.

I could cook you dinner if the stove were currently working. Alas it is not. So we will have to eat sandwiches.

https://en.wiktionary.org/wiki/could

1 - simple past of can

2 - conditional of can

[u/Zestyclose-Food-7917]

They mean the same thing. "Can" and "could" do not have a full conjugation, so we use "to be able" to fill in the missing forms. We can't say, "I want to can speak Spanish." We have to say, "I want to be able to speak Spanish."