In my earlier post, I have briefed you about the modal verbs. Now, we will discuss in detail how to use modals like Should, Ought to and must. These three modal verbs often sound similar and are used interchangeably in the sentences. Therefore, it is important to learn the correct usage of them.

It is used to express:

Duty or obligation

•          Children should always listen to their parents.
•           We should help each other.
•           You should keep your words.

Probability

•         The train should have left the platform now.
•         He should be in the office right now.

Opinion

•   You should choose first one rather than others.
•        We should plan a vacation next month.
•        The government should take measures on this issue.

Advice

•  You should check the expiry date before buying packed food.
• You shouldn’t eat junk foods daily. It’s not good for your health.

Criticism (in past tense)

Should+ have+ past participle

•        He should have informed me earlier.
•        She should have completed her assignment before deadline.

It is a semi-modal verb. It is used to express:

Moral obligation (general)

•   We ought to help our elders.
•    We ought to throw garbage in dustbins.

Probability (desire) (Not very much common)

• He ought to reach the library at this time.
•         You ought to apologize.

• Should is a modal verb whereas “Ought to “is a semi-modal verb also “To” is used after it.
• “Ought to” sound stronger and formal than “should”. So, we must take care of it.

1. She should be here by now.
2. She ought to be here by now. (stronger and annoying)

• “Should”is used to give advice or opinion and one can choose to follow or ignore It, whereas ought to is used when the  has to be followed.

1.  You should wear the helmet while driving.
2. You ought to wear the helmet while driving.

It is the strongest among all. It is used to express:

 Necessity

• You must work hard in exams time.
•  You must improve your handwriting.

Logical assumption

• Working with low facilities must be very difficult.
• Riya have a luxury car. She must belong to a wealthy family.

Rules

• All students must have identity cards with them.
• You must reach there on time.

Prohibition

• You must not use the calculator while your exam is going on.
• You must not smoke here.

Must refers to the present or the near future. To talk about the past, we use had to; must has no past form.

In informal English, often ‘Have to’ is used instead of must for rules and obligations.