Cambridge Grammar of English Hardback with cd-rom a comprehensive Guide

Be able to

404b

Be able to

often means the same as can when referring to abilities (

Û

381

), but it

is much less common. It is often used in situations where can is not grammatically

possible:

I might not 

be able to get an eyesight test for tomorrow.

(I might not can get an eyesight test for tomorrow.)

Will you 

be able to carry that big box all on your own?

[giving directions]

Can you see that white building down there? It’s just next to that.

(preferred to: Are you able to see that white building …?)

The negative of be able to is formed with not or (more formally) with unable:

[university science lecture]

The virus 

is no longer able to attach to a target cell. It’s therefore not able to

cause an infection. 

We have

n’t been able to contact her, I’m afraid.

Did anybody ask you why you 

were unable to attend?