Use of Can, Could and Able

When asking about a possibility it is important to connect that to can and its past form could. Most learners don’t know that grammatically could is the past form of can and that the same question could be asked in two ways but when someone asks with could instead of can it does not mean that the person is being asked about his abilities in the past, it is just a more polite form and is often connected to formal speech,

Able is distinctive from can because it is used to ask about a person’s capacity to perform an action. I have often used the analogy of a person in cast whose movement is restricted. The person can write even if he has his arm in cast if has learned it, only if his movement is restricted, he is unable to. This is a distinction that I find more current in Europe and less so in the US where can is used in both cases but then one loses the sense of knowing whether the activity is learnt or restricted.

On a scale of possibility and probability, can is on the top followed by my and then might is on the bottom when expressing how definite a person is on doing something. But I have also seen scales incorporating the use of will as being yet more definite and on top of can when referring to a person desire to do something. So if a person can do something as in I can be there, there is a good possible that he will do that but it does not mean he is definite on performing the action. If he uses will as in “I will be there” then he is definite.

May was used to ask the teacher to go to the bathroom as in “May I go the washroom?” because back then one had to address an older person differently. I don’t think that the same distinction is made today but if one wants to show respect then “can” would not be used. Might is going to be used to ask for something that is less likely than possible. It is as if the person knows ahead of time that the likelihood of him.

The same can be said for the difference between can and could as far as politeness is concerned; there is used to be more of a distinction years ago but today I person is less likely to differentiate between the two especially south of the border or in regions where the language has become more dilute.