Ability in tenses other than present and past

If we need to express ability in other tense combinations (e.g. the future or the present perfect), then the appropriate forms of be able to, manage to or succeed in must be used:

I'll be able to pass my driving test after I've had a few lessons

I've been trying to contact him, but I haven't managed to Can, referring to ability, skill, or perception, is usable in clauses after and when [> 14.4] to refer to the future:

If you can pass (or are able to pass) your driving test at the first

attempt, I'll be very surprised

Modals, etc. to express permission/prohibition

Expressing ability with 'can' and 'could' in the passive

Passive constructions with can and could, indicating ability, are

possible where the sense allows:

This car can only be driven by a midget

The lecture couldn't be understood by anyone present

The injured men could have been reached if heavy equipment had

been available during the rescue operation

11.18 'Can/could' = capability/possibility

Can + be + adjective or noun has the effect of 'is sometimes' or 'is often' and refers to capability or possibility. It can be replaced by be capable of + -ing, but not by am/is/are able to: It can be quite cold in Cairo in January (= It is sometimes - or often - quite cold.) He can be very naughty, (or 'a very naughty boy') [> 10.11] (When used for people, the effect is generally negative, even when the adjective is favourable: She can look quite attractive when she wants to — which implies she doesn't usually look attractive.)

Could has the same effect in the past: It could be quite cold in Cairo in January when I lived there (= It was sometimes - or often - quite cold.) He could be very naughty when he was a little boy

Could can also have a future reference in this kind of context:

It could be quite cold when you get to Cairo

Uses of modals, etc. to express permission and prohibition