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12.3 ability can, could versus be able to, manage, succeed 1.
Can is used to talk about a future ability provided that the decision is being made now. Note
will can is incorrect.
2. In cases where
can is not possible to talk about a future event, a form of
be able to is generally used.
3.
Could in the affirmative indicates
a habitual past ability, i.e. something that someone or something was able to do regularly
was able to can also be used in this context. Note like all modal verbs
could requires the infinitive without
to. 4. When describing an ability to do something on
one particular past occasion,
could is never used in the affirmative and interrogative forms. In both these cases, use a form of
to be able to, to succeed in or
to manage. 5. In order to avoid confusion with the conditional, to talk about past inabilities it is better to replace
could not with
did not manage to, did not succeed in, or
was / were notable to. 6.
To be able to replaces can in all other tenses and forms.
YES NO 1 I
can finish the paper by tomorrow. I
will can finish the paper by tomorrow.
2 I
will be able to speak better English when I have finished this course. I
can speak better English when I have finished this course.
3 The patient
could / was able to walk at the age of six months. The patient
could to walk at the age of six months.
4 I
managed / was able to finish the manuscript on time. I
could finish the manuscript on time. I
succeeded in finishing the …
5 They
didn’t manage / were unable Share with your friends: 
