The verbs be ( am, was, is etc ) have and do, when used with ordinary verbs are called auxiliary verbs or helping verbs. They are called primary auxiliaries verbs because they help to form certain important grammatical constructions such as, tenses, passive forms, questions and negatives etc.
The verbs can, could, may, might, will, would, shall, should, must, and ought are called modal verbs or modals. They are used before ordinary verbs and express the meanings such as permissions, complaints, possibility, certainty and necessity. Need and dare is can sometimes be used like modal verbs.
The modals are also called Defective Verbs because some parts are wanting in them. They don't have -s in the third person singular form and they have no infinitive and -ing forms.
The auxiliary do is used
1. To make verbs negative and questions,
• He doesn't work.
• Does he work?
2. To avoid repetition of a previous ordinary verb.
• Do you know him? Yes, I do.
• You met him. Didn't you?
3. To emphasize the sentences,
• You do look pale.
• I told him not to go, but he did go.
4. To make a request or invitation more persuasively.
• Do be quiet.
• Oh, do come! It's going to be such fun.
The auxiliary be is used:
1. In the formation of the continuous tense and passive.
• He was working.
• The gate was opened.
2. To indicate a plan, arrangement, or agreement.
• I am to see him tomorrow.
• We are to be married next month.
3. To denote command.
• Mother says you are to go to market at once.
• You are to write your name at the top of each sheet of paper.
The auxiliary have is used
1. To form the perfect tense.
• He has been working since yesterday.
• He has finished his work.
2. With the infinitive to indicate obligation
• I have to be there for support.
• He has to move the furniture by himself.
3. To form negatives and questions with do or does.
• They have to go. - They don't have to go. - Do they have to go?
The modal shall is used
1. To express the future when the subject is I or WE
• I/We shall leave for Bombay this afternoon.
2. To express command and threat,
• They shall suffer for this.
• He shall report for job tomorrow.
3. In questions with I or We , express an offer or suggestion,
• Will I be alright tomorrow?
• Will you please pass me the paper?
The modal should is used
1. As the past tense of shall in indirect speech,
• He said, "The worker shall report for duty on Monday." ( Direct speech )
• He said that the worker should report for duty on Monday. ( Indirect speech )
2. To express obligation or advisability,
• People should not tell lie.
• You should take exercise regularly.
3. To express logical necessity or probability,
• They should be home by now.
• Our suits should be ready by evening.
4. To express probable condition
• Should I see him, I will speak to him.
5. To express for permission,
• I should like to say that I haven't done anything wrong against the rule.
The modal will is used
1. In the formation of future tense,
• My brother will leave for Bombay for tomorrow.
• I will kill him day after tomorrow.
2. To express willingness or polite request,
• I will help you as far as I can.
• Won't you sit down?
3. To express intention or promises,
• I will come as soon as I can.
• I won't speak for more than half an hour.
4. To express determination,
• We will fight till the end.
• We will root out corruptions.
5. To express prediction,
• If you step on a snake, it will bite you.
• He will never tell a lie.
The modal would is used
1. As the past tense of will or shall in indirect sentence.
• "I shall send for the doctor," said Mr. Sastri.
• Mr. Sastri said that he would send for the doctor.
2. To express a habitual or characteristic activities in past,
• Once every week he would go for a swim in the sea.
• Every morning Gandhiji would go for a long walk.
3. To express a suggestion or a polite request,
• Would you care for a glass of lemonoud?
• Would you close that door?
4. To express a wish or preference with rather for some kind of comparison,
• I would rather starve than beg.
• I would rather have a glass of water than coffee or tea.
5. To express the imagined result of an imagined or supposed condition,
• I would build a hospital if I won a lottery.
• If I were a cosmonaut, I would take you to the moon.
6. To express wish or preference with like,
• I would like to ask you something.
• He says he would like to go with you
The board of directors shall be responsible for payment to stockholders.
The college president shall report financial shortfalls to the executive director each semester."
You really shouldn't do that.
If you think that was amazing, you should have seen it last night.
She doesn't work here anymore.
Do you attend this school?
Does he work here?
It should rain tomorrow.