The finites which express the mode or manner of the actions denoted in the principal verb are termed as Modals. This class of helping verbs not only assists in forming questions and negatives, but expresses a wide range of meanings also. These helping verbs are can, could, will, would, shall, should, may, might, must, ought to, have to, has to and had to. These are known as modal auxiliaries. They express the degree of certainty of the action in the sentence or the attitude or opinion of the writer/speaker concerning the action. Need, dare and used to are called semi-modals.

Nature of Modals

Modals are never used alone.

Examples:
a) I can upon the harmonium.
b) I can play upon the harmonium.

So, modals have a principal verb with them.

Modals don’t change according to the number of person of the subject.

Examples:
a) I can play.
b) He can play.
c) We can play.
d) They can play.

Modals don’t have the infinitive form. We can’t place ‘to’ with them in order to use them in a sentence.

Examples:
a) We must to get there before them.
b) We must get there before time.

Functions of Modals

Will

i) To show promise, intention, willingness, determination with the first person (I, we) 

Examples:
a) I will give you a gift of your choice. (promise)
b) We will help you. (willingness)
c) I will change the system of our organisation. (determination)

ii) To express request, invitation, insistence, assumption, characteristic or habit

Examples:
a) Will you please help me? (request)
b) She will be in the school during school hours. (assumption)
c) The lion will usually kill other animals. (characteristic, habit)

Negative Form of will : Will not/Won’t

Examples:
a) I will not spend my pocket money.
b) She won’t eat unhygienic food.
c) They won’t win the match.
d) My friend will not attend the party.

Would (Past form of ‘Will’)

i) It expresses the past form of ‘will’

Examples:
a) He informed me that he would dance at my marriage function.
b) The problem was how he would reach there.

ii) To express past habit

Examples:
a) He would drink a cup of coffee in the morning.
b) My father would get up early in the morning.

iii) For request

Examples:
a) Would you please give me your bike?
b) Would you like to spend this evening with me?

iv) To express wish

Examples:
a) I wish she would be healthy.
b) You would be an engineer.

v) To express an imaginary condition

Examples:
I would have a big house if I earned Rs.10 crore every year.

Negative Form of Would : Would not/Wouldn’t

Shall

i) To ask for suggestion, request, advice with the first person (I, We) in the interrogative

Examples:
a) Shall we start the class? (advice)
b) Shall I have a cup of coffee from your shop? (request)
c) Shall we open a new shop? (suggestion)

ii) In the second and third person to indicate threat, warning, command, promise, assurance and determination

Examples:
a) If you sit with bad boys, you shall be punished. (threat)
b) You shall got now. (command)
c) She shall get a bicycle. (promise)

Negative Form of Shall : Shall not/Shan’t

Examples:
a) She shall not sing tomorrow.
b) They shall not win the match.
c) My friend shan’t be dismissed.

Should (Past form of ‘shall’)

i) To express duty or obligation

Examples:
a) I should help my friends. (duty)
b) You should not be lazy. (obligation)
c) You should respect your elders. (duty)

ii) To give or take permission.

Examples:
a) May I come in?
b) Yes, you may come in.

iii) To wish or pray

Examples:
a) May you get well soon!
b) May God bless you with a child!

iv) To show a purpose

Examples:
a) My friend is joining a new company so that he may achieve his target.
b) He is working hard so that he may win.

Negative Form of May : May not/Mayn’t

Examples:
a) It may not rain today.
b) She mayn’t attend the meeting.

Might (Past form of ‘may’)

i) To express less possibility

Examples:
a) He might help us.
b) She might be a winner in the competition.

ii) For permission

Examples:
a) Might I being to reveal the truth?
b) Might I start speaking?

iii) To express a guess

Examples:
That might be Rohit.

Negative Form of Might : Might not/ Mightn’t

Examples:
a) It might not rain.
b) She mightn’t talk to me this evening.

Must

i) To express necessity or obligation

Examples:
a) You must take part in the competition.
b) We must love our motherland.

ii) To indicate assumption or conclusion

Examples:
a) She must be here in the evening.
b) Mr AK Gupta must be a good teacher.

iii) In case of prohibition.

Example:
You must not bunk school.

Negative Form of Must : Must not/Mustn’t 

Examples:
a) You must not play in sunlight.
b) You must not write your name on the walls.
c) You mustn’t make a fuss over this.

Have to/ Has to/Had to

i) To express obligation or compulsion (While talking about rules, laws)

Examples:
a) I have to reach school early.
b) She has to work late in the office.
c) They had to follow the instruction.

Negative Form of Have to : Don’t have to

Examples:
a) I don’t have to cook the food at home.
b) She doesn’t have to work till late in the office.

Ought to

i) To express moral obligation or duty

Examples:
a) You ought to respect your parents.
b) You ought to serve the nation.
c) We ought to help our relatives.
d) We ought to speak the truth.

ii) To give advice

Examples:
You ought to study hard to achieve success.

Negative Form of Ought to : Ought not to/ Oughtn’t to

Examples:
a) You ought not hate your neighbours.
b) You oughtn’t to insult your elders.

Use of ‘Need’, ‘Need to’, ‘Dare’ and ‘Used to’

Need and dare are considered semi-modals because they can be used either as modal auxiliaries or as main verbs.

Need/Need to

As a modal auxiliary verb in negative terms, it indicates absence of obligation. It expresses the speaker’s authority or advice and is used for the present and the future. e.g. You needn’t type this letter.

i) The interrogative is formed by inversions.
e.g. Need I speak to him?

ii) Its past is needed to in the affirmative sentence, need not have in the negative and need have in the interrogative.

Examples:
a) Need I have gone to him ? ( Interrogative in the past)
b) I needed to go to him. (Affirmative in the past)
c) You needn’t have gone to meet him. (Negative in the past)
d) You need to go to the barber – your hair are too long. (Affirmative in the future)

Dare

As a modal auxiliary, dare refers to being bold and courageous. The negative is formed by dare not and the interrogative by inversion.

Examples:
a) Dare we talk to them?
b) I dare not disturb them.

Used to

i) A discontinued habit or a past situation which is no more in the present.
e.g. He used to drink daily. (Now he does not drink)

ii) Something existing in the past.
e.g. This used to be a dense jungle before.