CAN is one of the most commonly used modal verbs in English. It can be permission and to show possibility or impossibility.Modal use :-
General Ability I can ride a horse.
Ability during a specific event With a burst of adrenaline, people can pick up cars.
Opportunity I have some free time. I can help her now.
Permission She can not stay out after 10 p.m.
Request Can you hand me the stapler?
Possibility Any child can grow up to be President.
COULD is used to express possibility or past ability as well as to make suggestions and requests. COULD is also commonly used in conditional sentences as the condition form of CANModal use : -
Possibility John could go to jail for stealing the money.
Suggestion you could spend your vacation in Shimla.
Past Ability I could run ten miles in my twenties.
Polite Request Could I've something to drink?(near future)
Conditional of can If I had more time, I could travel around the world.
MAY is most commonly used to express possibility. It can also be used to give or request permission, although this is being used less common.Modal use :-
Possibility Jack may not get upset, even if you tell him the truth.
Give Permission You may leave the table when you finish your dinner.
Request Permission May I make a phone call?(near future)
MIGHT is most commonly used to express possibility. It is also used after Conditional sentences. English speakers can also use MIGHT to make suggestions or requests, although this is less common in American English.Modal use :-
Possibility Your purse might be in the living room.
Conditional of May If I entered the contest, I might actually win.
Suggestion You might try the cheese cake.
Request Might I have something to drink? (near future)
MUST" is most commonly used to express certainty. It can also be used to express necessity or strong recommendation, although native speakers prefer the more flexible form "have to." "Must not" can be used to prohibit actions, but this sounds very severe; speakers prefer to use softer modal verbs such as "should not" or "ought not" to dissuade rather than prohibit. Modal use :-
Certainty This must be the right address.
Necessity You must have a permit to enter the national park.
Strong Recommendation You must take some time off and get some rest.(emphatic advise)
Prohibition Jenny, you must not play in the street! ( near future)
"Ought to" is used to advise or make recommendations. "Ought to" also expresses assumption or expectation as well as strong probability, often with the idea that something is deserved. "Ought not" (without "to") is used to advise against doing something, although Americans prefer the less formal forms "should not or "had better not.Modal use :-
Recommendation, Advice You ought to stop smoking.
Advice against something Mark ought not drink so much.
NOTICE There is no To.
Assumption, Expectation, Probability - She ought to receive the package tonight.
John ought to get the promotion. (It is expected because he deserves it)
"Shall" is used to indicate future action. It is most commonly used in sentences with "I" or "we," and is often found in suggestion such as "Shall we go?" "Shall" is also frequently used in promises or voluntary actions. In formal English, the use of "shall" to describe future events often expresses inevitability or predestination. "Shall" is much more commonly heard in British English than in American English; Americans prefer to use other forms, although they do sometimes use "shall" in suggestions or formalized language. Modal use :-
Suggestion Shall we begin dinner?
Future Action I shall be there by 8:00.
Volunteering, Promising I shall take care of everything for you.
Predestination He shall become our next king.
Inevitability Man shall explore the distant regions of the Universe.
"Should" is most commonly used to make recommendations or give advice. It can also be used to express obligation as well as expectation.Modal use :-
Recommendation, Advisability People with high cholesterol should eat low fast food.
Obligation We should be at work before 9:00.
Expectation He should be in New York by next week. His new job starts on Monday.
"Should" can also express something between recommendation and obligation. "Be supposed to" expresses a similar idea and can easily be used in the past or in negative forms.
Will" is used with promises or voluntary actions that take place in the future. "Will" can also be used to make predictions about the future. For more information on using "will" and associated exercises, visit the Simple Future Tense.Modal use :-
Future Action Prediction He thinks it will rain tomorrow.
Voluntary Action I will make dinner tonight.
Promise I promise that I will write you every single day.
"Would" is most commonly used to create conditional verb forms. It also serves as the past form of the modal verb "will." Additionally, "would" can indicate repetition in the past.Modal use:-
Past of will He told me that he would be here before 8:00.
Conditional If I were president, I would cut the cost of education.
Repetition in Past When I was kid, I would always go to the beach.