Modal auxiliaries are verbs such as can, must, could, would, etc. which are used with main verbs to express such ideas as possibility, permission, necessity, obligation, etc.
Characteristics of Modal Verbs
1. Must and have to:
(i) Must is used to express obligation:
(ii) It is used to express compulsion, e. ordering someone to do something because it is necessary or important to do so:
(iii) It is used for saying that something is probably true because nothing else seems possible:
(iv) The negative form of must (must not) is used for prohibition:
(v) It is used to give emphatic advice:
Must and have to:
Have to, like must, expresses obligation in the present while had to does so in the past. Must expresses an obligation imposed by the speaker. Have to/Had to expresses external obligations—an obligation by some authority or circumstances.
Had to is used when describing something belonging to the past.
These two verbs have the following forms:
|Present||must have/ has to|| must I?|
have I to / has he to?
| haven't to|
|Future Time Reference||must, shall/will have to|| shall have I to?|
will have you to?
| I shall not have to|
you'll not have to
|Past||had to||had i do?||I hadn't to|
Have to and had to have alternative negative and interrogative forms:
| haven't to or don't have to|
hadn't to or didn't have
| have I to?|
do I have to?
|Past Tense:|| hadn't to|
didn't have to
| had I to ?|
did I have to?
Have you to obey his orders?
Do you have to obey his orders?
Had you to work on Sundays?
Did you have to work on Sundays?
Do you have to mind your watch every day?
Did you have to pay customs duty on your watch?
2. Have to/Had to:
(i) Have to expresses obligation and necessity in the present. Had to does so in the past:
(ii) Have to and had to are used for giving advice:
(iii) Have to and had to are used to draw a logical conclusion:
(iv) Have to is used for supposition or to describe something based on possible ideas or situations:
(v) Have to is used to indicate that something is very important or necessary:
(i) Should is the past tense of shall. In indirect form of speech ‘shall’ changes into should:
(ii) Should is used to express obligation, duty, etc.
(iii) Should is used to give advice or suggestion:
(iv) Should is used to express purpose:
(v) Should is used to state imaginary results:
(vi) Should is used to express polite requests:
As a modal verb, need is usually followed by an infinitive without ‘to’:
The modal verb need is mainly used in questions and negatives, which are formed without ‘do’:
Need I go now? You need not go.
The negative need not is often shortened to needn’t in conversation and informal writing. Need does not change its form, so the third person singular of the present tense does not end in’ —s’:
He need not go there.
The modal verb need has no past tense. But it can be used in the pattern followed by a past participle:
Need not have/needn’t have
You needn’t have waited for me.
The negative and interrogative forms of the past tense are:
Did not (didn’t) need and did I need?
In the present and future tenses, the negative and interrogative can be formed in either of the two ways:
|Present Tense:|| need not (needn't)|
or don't / doesn't need
| need I?|
or do I need / does he need?
or need I? shall I need?
will he need?
| Future Time:|
| need not|
or shan't / won't need
| or need I? shall I need?|
will he need?
(i) The negative need expresses absence of obligation:
(ii) Need is used to express obligation or necessity:
(iii) Need not + perfect infinitive is used to express an unnecessary action which was performed:
Ought is usually followed by ‘to’ and an infinitive:
It does not change its form so that the third person singular form does not end in ‘-s’:
It can be used as a present, past, or future tense.
The negative is ought not (oughtn’t) and the interrogative is ought I?, Ought you?, Ought he?, etc:
(i) Ought to is used for expressing what is the right or sensible thing to do, or the right way to behave:
(ii) Ought to is used when we believe strongly or expect that something will happen:
(iii) Ought to see/hear/meet, is used for emphasising how good, impressive or unusual something or someone is:
(iv) Ought to have is used when we realise that we did not do the right thing in the past:
Ought, must, have to, and should:
Note: Ought is used to express the subject’s obligation or duty. But it indicates neither the speaker’s authority as with must, nor an outside authority as with have to. The speaker is only reminding the subject of his duty. Besides this, he is giving advice or indicating a correct or sensible action.
Ought can be used in exactly the same way as should:
You ought to/should obey your parents.
Have to and must:
You have to be regular. (These are the rules.)
You must obey your teachers. (The speaker insists on it.)
You have to take this medicine. (The doctor insists on it.)
You must take this medicine. (The speaker insists on it or It is the speaker’s emphatic advice.)
You mustn’t drink this, it is poison, (prohibition)
You oughtn’t smoke so much. (It is not right or sensible.)