By Rob Lane
Ability can be expressed using modal verbs and phrases. Learners often prefer to use be able to because it is the easiest to form. As learners progress, they begin to use can, could, and managed to. It is at this point that learners encounter usage rules and often make mistakes. In this article, I will focus on the most commonly used modals for ability and the most typical mistakes. While the present forms are simple, the past forms have particular rules which must be followed. The most important rules relate to general ability and specific ability.
General ability means that a person had the ability to do something at all times and in all situations.
Specific ability means that the person had the ability to do something in a specific situation or at a specific time.
Forms in this Article
Can, could, be able to, and managed to.
Is/am/are able to + main verb
Thomas is able to play the piano.
Catherine is not able to play the piano.
Can + main verb
Catherine can play the flute.
Thomas can’t play the flute.
Both of these forms may be used, in positive or negative, for general or specific ability.
Was/ were able to + main verb
Thomas was able to play the piano when he was a boy.
Catherine was not able to play saxophone when she was a girl.
This form may be used, in positive or negative, for general or specific ability.
Could + verb
When Jane was in Austria, she could speak German.
Could, in positive, is only used for general ability.
When Jane was very young, she couldn’t speak German.
Couldn’t is used for general or specific.
Gerry lost control of his car but managed to avoid a crash.
This form is only used for specific ability: one time, one situation.
The typical mistakes learners make are to use could for past positive specific ability.
My friend’s phone was engaged all day yesterday. Finally, late in the evening, I could speak to him.
In this sentence, we should use I was able to speak to or I managed to speak to him.
When Jim was a boy he could climb trees very well (This was a general ability). However, there was one tree that was very tall and he couldn’t climb it (the general specific rule is only for could in positive so there is no issue here). One day, when he was feeling very energetic, he was a able to/ managed to climb the tree (specific time, situation).
Practice the forms in a grammar exercise book.
Write texts or using the different forms.
Write dialogues similar to practical conversations.