Ways of referring to time when using modals are explained in paragraphs 5.107 to 5.114. Ways of using modals to say whether something is possible are explained in paragraphs 5.115 to 5.151. Ways of using modals when interacting with other people are explained in paragraphs 5.152 to 5.220.
Expressions that can be used instead of modals are described in paragraphs 5.221 to 5.245. Semi-modals are explained in paragraphs 5.246 to 5.256.
The main uses of modals
5.94 Modals are mainly used when you want to show your attitude towards what you are saying, or when you are concerned about the effect of what you are saying on the person you are speaking or writing to.
attitude to information
5.95 When you are giving information, you sometimes use modals to show how certain you are that what you are saying is true or correct.
For example, if you say Mr Wilkins is the oldest person in the village, you are giving a definite statement of fact. If you say Mr Wilkins must be the oldest person in the village, the modal must shows that you think Mr Wilkins is the oldest person, because you cannot think of anyone in the village who is older than Mr Wilkins. If you say Mr Wilkins might be the oldest person in the village, the modal might shows that you think it is possible that Mr Wilkins is the oldest person, because he is very old.
attitude to intentions
5.96 You can use modals to show your attitude towards the things you intend to do, or intend not to do. For example, if you say I won’t go without Simon, you are expressing strong unwillingness to go without Simon. If you say I can’t go without Simon, you are saying that there is a special reason for not going without him. If you say I couldn’t go without Simon, you are saying that you are unwilling to go without Simon, because to do so would be wrong, or impossible because of the circumstances.
attitude to people
5.97 When you use language, you are affecting and responding to a particular person or audience. Modals are often used to produce a particular effect, and the modal you choose depends on several factors, such as the relationship you have with your listener, the formality or informality of the situation, and the importance of what you are saying.
For example, it would normally be rude to say to a stranger Open the door, although you might say it in an emergency, or you might say it to a close friend or a child. Normally, you would say to a stranger Will you open the door?, Would you open the door?, or Could you open the door?, depending on how polite you want to be.
use in sentences containing more than one clause
5.98 Modals have special uses in three kinds of sentence containing more than one clause:
Wilson dropped a hint that he might come.
I felt that I would like to wake her up.
For more information about reported clauses see Chapter 7.
If he had died when he was 50, he would have died healthy.
If only things had been different, she would have been far happier with George.
For more information about conditionals see paragraphs 8.25 to 8.42.
He stole under the very noses of the store detectives in order that he might be arrested and punished.
He resigned so that he could spend more time with his family.
For more information about purpose clauses see paragraphs 8.47 and 8.48.
Special features of modals
form of following verb
5.99 Modals are followed by the base form of a verb.
I must leave fairly soon.
I think it will be rather nice.
They ought to give you your money back.
Note that ought is sometimes regarded as a modal, rather than ought to. Ought is then said to be followed by a to-infinitive.
5.100 Sometimes a modal is followed by the base form of one of the auxiliary verbs have or be, followed by a participle.
When a modal is followed by be and an -ing participle, this shows that you are talking about the present or the future.
People may be watching.
You ought to be doing this.
The play will be starting soon.
When a modal is followed by have and an -ed participle, this shows that you are talking about the past.
You must have heard of him.
She may have gone already.
I ought to have sent the money.
In passive structures, a modal is followed by be or have been and an -ed participle.
The name of the winner will be announced.
They ought to be treated fairly.
Such charges may have been justified.
A modal is never followed by the auxiliary verb do, or by another modal.
no inflections
5.101 Modals do not inflect. This means there is no -s form in the third person singular, and there are no -ing or -ed forms.
There’s nothing I can do about it.
I am sure he can do it.
I must leave fairly soon.
Could is sometimes thought to be the past tense of can. This is discussed in paragraphs 5.110 and 5.111.
negatives
5.102 Negatives are formed by putting a negative word such as not immediately after the modal. Can not is usually written as one word, cannot.
You must not worry.
I cannot go back.
In the case of ought to, you put the negative word after ought.
He ought not to have done so.
News organizations ought not treat them so poorly. (American)
After could, might, must, ought, should, and would, not is often shortened to -n’t and is added to the modal.