Main verbs have only two tenses, namely present and past (e.g. go; went). However these two tenses alone are by themselves cannot express 1)aspect – (completeness, incompleteness, continuity, completed with relevance to the present), 2) negation, 3) question, 4) passivization of voice 5) numeral value of subject (singular/ plural), and 6) gender
A set of verbs which help main verb in these functions as stated above are called auxiliary or helping verbs.
Thus, to express aspect we need ‘be’ verb (is, are, am, was, were), has, have, had, has been, have been, had been, will be, will have, will have been, would have, was going to , were going to
For negation and question, apart from ‘be’ verb, ‘have’ verb (has, have, had), and will we also need ‘do’ verb (do, does, did) to negate and question main verb.
The bananas are not ripe yet; She didn’t eat anything; We won’t eat in any restaurant; He had not slept for two nights; I haven’t thought about my retirement plan yet; Has everyone eaten? Does she teach science for grade 12? Will you be here by 10 o’clock tomorrow?
We also need ‘be’ verb and ‘have’ verb for passive voice.
My wife supports me. > I am supported by my wife.
Industries are polluting the river. > The river is being polluted by the industries.
The maid broke the vase. > The vase was broken by the maid.
The police have arrested the culprits. > The culprits have been arrested by the police.
Thus ‘be’ verb, ‘have’ verb, ‘do’ verb and ‘will’ are auxiliary or helping verbs. Except for ‘will’ the rest are known as primary auxiliary verbs, since the auxiliary verb ‘will’ lacks in certain properties of be, do and have which are as follows:
1) It is gender-agnostic and doesn’t change with singular or plural such as she, he, they.
2) It cannot function to express aspect on its own. Aspect can be expressed only with help of ‘be’ or ‘have’ such as will be, will have, would have
3) Unlike primary auxiliaries, ‘will’ cannot become main verb.
She is a school teacher; Cow is a mammal [here ‘is’ is not an auxiliary but main verb]
I have work to do; She has two kids [‘have’ as main verb]
I did my best. Have you done your home work? [‘do’ as main verb]
4) ‘will’/’shall’ are used to express action/ activity in future since in English a verb does not have future tense. This is in fact the only reason for ‘will’/’shall’ is treated as an auxiliary.
5) Apart from being auxiliary, ‘will’ is also used as modal to express promise, typical nature/ behaviour, and willingness
Modal Verbs
Now that we know the role of auxiliary verb, we must also know their limitations when it comes to use main verb to express ability, belief, guess/ assumption, imagination, obligation, promise, permission, possibility, necessity, certainty, request, offer, suggestion, opinion, hypothesis, usual behaviour etc. Only modal verbs can ad these meanings to the main verb.
These verbs are can, may, will, could, might, would, should, must – all of which can also take ‘have’ for aspect
Unlike auxiliary verbs modal verbs do not conjugate for third-person singular subjects; they do not have a simple past tense, present participles (verb-ing), or past participles (verb-ed) and they cannot form infinitives (to-verb).
Semi modal verbs are: dare, need, have to, ought to, used to etc.
‘dare’ and ‘need’ like modal verbs take bare root verb and but unlike main modal verb can also function as main verb and able to take nouns and infinitives as objects and to conjugate for person, tense, and number.
However have to, ought to, used to are semi modal because of ‘to’ but unlike dare, need they cannot function as main verb.
Dare
When dare is used as a semi-modal verb, it means “to be brave, reckless, or rude enough to do or try something. It is mostly used in negative or interrogative sentences.
If he dare cross me again, I’ll make sure he pays dearly for it.[not dares]
In a society of individualists nobody dare admit to being a conformist.
How dare she talk to me like that?
Dare he meddle with the laws of nature?
They daren’t give him a reason to be angry.
Need
Need is almost always used in negative or interrogative sentences to express a lack of obligation or necessity.
No one need know about this shameful issue.
He needn’t have called my mother to cross check.
You needn’t worry about my career plans.
Nothing need change because of postponement.
Need we be cautious?
Need I conduct the experiment to be sure of result?
Ought to
Ought to is commonly compared to should because it expresses that something is viewed as correct, preferable, or necessary—or as probable, likely, or expected. It can also be used to ask for or offer advice about something.
Airfares being so high, in-flight meals ought to be free.
We ought to reach airport at least 3 hours in advance before departure.
I think we ought to cancel the trip.
You ought to read this book for an authentic and comprehensive knowledge.