The Modal Verbs can, could, to be able to
Modal verbs are used to express ideas such as possibility, intention, obligation and necessity in the English language. Also, modal verbs are a small group of verbs which convey the speaker's opinion about or attitude towards what is being expressed. Modal verbs include “can”, “could”, “will”, “would”, “shall”, “should”, “ought to”, “dare” and “need”.
The most important modal verbs in the English grammar are “can”, “may” and “must”.
Differences between "can", "could" and "to be able to"
- The word “can” is used for present tense and for the action that can be done. Whereas the word “could” is used for the past. Something that you could have done but you did not do. “Can” and “could” are both what are called auxiliary verbs. We use “can” to talk about possibility and ability, make requests and ask for or give permission. We use “could” to talk about a past ability or possibility or to make requests.
- "to be able to" is the replacement for „can“ or „could“ in every tense. After "to be able to" the base form follows.
-
- They are able to swim back to the island.
- The girls are able to ride the horse.
- She has not been able to call you.
- None of us has been able to cross the river.
- ATTENTION: Both "can" and "could" express ability and permission. "to be able to + base form" only expresses an ability.
| Permission | Ability |
|---|---|
| Susi can speak to him. | Tom only speaks Spanish, but Susi can speak to him. |
| ..., but Susi is able to speak to him. | |
| James could eat 2 portions. | I couldn't eat because I just had dinner. |
| I wasn't able to eat because ... |
- In if-sentences and formal questions "could" is used.
- Could you close the window, please?
- Susi would come to visit us if she could.
- Negation:
| can | cannot/can't | could | could not/couldn't |
|---|---|---|---|
| am able to | am not able to | was able to | was not able to |
| is able to | is not able to | were able to | were not able to |
| will be able to | will not be able to | had been able to | had not been able to |
| have been able to | have not been able to | has been able to | has not been able to |
These aspects are relevant for all modal verbs:
- Modal verbs do not occur alone. They are used in connection with a main verb, with the exception of short answers. In this case the main verb occurs always in the base form without “to”.
- Modal verbs do not occur in every tenses and forms, as follows:
- Infinitive (base form, 1st form)
- Past form (except "could")
- Past Participle
- Questions with modal verbs do not include "do - does - did".
- Modal verbs are the same used with each person. There are no exceptions.
- Every modal verb has its replacement to express them in other tenses.
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