what is differences among must ,should and ought to?

Question

advanced grammer

Answer 1

MUST
1. Used to express necessity
Example: I must earn some extra money
Example: Must you leave so soon?

2. Used to express duty or obligation.
Example: You must help him

3. Used to express certainty.
Example: You must be Charles

4. Used to express determination.
Example: I must remember to go to the bank

5. Used to express probability.
Example: She must be there by now

6. Used to express inevitability.
Example: We must all die some time

7. Used to express an invitation or suggestion. Also used with the main verb merely implied.
Example: You must come and see us soon
Example: You must read her other books

SHOULD
1. Expressing: obligation, duty or recommendation; ought to.
Example: You should brush your teeth regularly

2. Expressing: likelihood or probability.
Example: He should have left by now

3a. Expressing: condition;
Example: If she should die before you, what would happen?
3b. Expressing the consequence of a condition.
Example: I should never be able to live with myself if that happened

4. Expressing a past tense of shall in reported speech.
Example: I told them I should be back soon

5. Expressing statements in clauses with that, following expressions of feeling or mood.
Example: It seems odd that we should both have had the same idea

6. Expressing doubt or polite indirectness in statements
Example: I should imagine he left
Example: I should like to thank you all for coming.

7. literary Expressing purpose.
Example: in order that we should not have to leave


OUGHT
1. Used to express: duty or obligation.
Example: You ought to help if you can

2. Used to express: advisability.
Example: You ought to see a doctor

3. Used to express probability or expectation.
Example: She ought to be here soon

4. Used to express shortcoming or failure.
Example: He ought to have been here hours ago

5. Used to express enthusiastic desire on the part of the speaker.
Example: You really ought to read this book

6. Used to express logical consequence.
Example: The answer ought to be…..

Answer 2

Must is an imperative. It is a command. Should is a request and is used as an auxiliary. Ought implies moral duty.

Answer 3

must
- be necessary or be certain,
-to be compelled to do something because of a rule or law
-used to make suggestions
-to intend or be determined to do something
-something that is essential or obligatory

should
- expressing desirability,expressing likelihood or probability or expressing conditions or consequences
-would
-reporting past viewpoint about future
-used to soften harsh words

ought to
-indicates that somebody has a duty or obligation to do something or that it is morally right to do something
-indicates that something is important or a good idea
-indicates probability or expectation
- indicates a desire or wish
-indicates that something should be the case but may not be

Answer 4

Must communicates a need to do something.

Should and ought to are suggestions for action.

Answer 5

must, should, and ought to are called modal verbs.
Here's a link that tells you about all 3 forms, let's you practice, then gives you a test to see how much you've learned.
http://www.englishpage.com/modals/oughtto.html
Good luck!

Answer 6

If you will investigate MODAL AUX verbs you will find out. It's very easy and you will understand the difference. xxx I used to teach grammar. It's easy once you get the hang of it.

Answer 7

must is an imperation. the rest only indicate possibilities.