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be able to

Although we look at be able to here, it is not a modal verb. It is simply the verb be plus an adjective (able) followed by the infinitive. We look at be able to here because we sometimes use it instead of can and could.

We use be able to:

Structure of be able to

The basic structure for be able to is:

subject + be + able + to-infinitive
  subject main verb
+ I am able to drive.
- She is not able to drive.
? Are you able to drive?

Notice that be able to is possible in all tenses, for example:

Notice too that be able to has an infinitive form:

Use of be able to

Be able to is NOT a modal auxiliary verb. We include it here for convenience, because it is often used like "can" and "could", which are modal auxiliary verbs.

be able to for ability

We use be able to to express ability. "Able" is an adjective meaning: having the power, skill or means to do something. If we say "I am able to swim", it is like saying "I can swim". We sometimes use be able to instead of "can" or "could" for ability. Be able to is possible in all tenses - but "can" is possible only in the present and "could" is possible only in the past for ability. In addition, "can" and "could" have no infinitive form. So we use be able to when we want to use other tenses or the infinitive. Look at these examples: