Can vs. be able to

[fatama]

English Language Tests, Intermediate level

ESL/EFL Test #120 "Conditional Tenses", question 9

If I pay you twice as much, will you ......... to finish by Tuesday?

(a) are able
(b) is able
(c) be able
(d) can be able

English Language Tests, Intermediate level

ESL/EFL Test #120 "Conditional Tenses", answer 9

If I pay you twice as much, will you be able to finish by Tuesday?

Correct answer: (c) be able

Your answer was: incorrect
If I pay you twice as much, will you can be able to finish by Tuesday?
_________________________

if ianswer be able it will not be aquestion but if i use can be able it will be in the question form,, so please explaine for me more

fatma an english learner

[Alan]

Hi Fatma,

I must explain that can is a so-called defective verb, which means it doesn't have the usual parts that other verbs have. There is no infinitive for can and so we have to use a substitute - be able. When we want to make a question with can, we say either:

Can you help me?

or

Are you able to help me?

In the future form the only possibility is:

Will you be able to help me?

But you do not use can together with be able.

Alan
_________________
English as a Second Language
You can read my ESL story Progressive Forms