Should and ought to

have only one form which is not changed in reported speech. They are very much alike in meaning and they are nearly always interchangeable. Should is followed by the infinitive without the particle “to”, ought is followed by the infinitive with the particle “to”. These modal verbs express:

1. MODAL OBLIGATION OR DUTY which may not be fulfilled. (in all kinds of sentences)

Should + Non-Perfect Infinitive refers the action to the present or future.

Ought + Non-perfect Infinitive refers the action to the present or future.

You ought to/should help your friend. He is in trouble.

Ought she to help him? Should she help him?

He oughtn’t to/shouldn’t do it.

Should/ought to + Perfect Infinitive shows that a desirable action was not fulfilled and implies reproach, criticism, regret.

You ought to/should have told me about it.

Shouldn’t/oughtn’t to + Perfect Infinitive shows that an undesirable was fulfilled, something wrong has been done and it is now too late to change it (= criticism of the past action).

You oughtn’t to/shouldn’t have interfered.

2. ADVISABILITY, DESIREABILITY (in all kinds of sentences, usually with Non-Perfect Infinitive)

You ought to see a doctor.

You should not read in bed at all.

Note: It is sometimes difficult to discriminate between the first and the second meaning.

Synonyms: I advise you to do…; I advise you not to do…; I recommend you to do…; I urge you to do…; It’s advisable for you to do…; I would advise you to do…

3. PROBABILITY, something naturally expected (in the affirmative and negative sentences, generally with the Indefinite Infinitive)

This dish ought to/should be very delicious as it has been prepared by Mother.

This dish is very delicious. It ought to/should have been prepared by Mother.

The guests shouldn’t come for another hour. (Гості навряд чи прийдуть раніше, ніж через годину.)

Note: Must is more frequent in this meaning than should/ought to.

ONLY SHOULD IS USED TO EXPRESS:

1. INSTRUCTIONS and CORRECTIONS (in all kinds of sentences with the Indefinite Infinitive)

You should use the definite article in this sentence.

You should take this medicine three times a day before your meals.

2. for EMOTIONAL COLOURING (with the Indefinite Infinitive) in the following cases:

1. in rhetorical questions beginning with “why”:

Why should I help him?

Why shouldn’t I join them?

2. in object clauses beginning with “why”:

I could not understand why he should be angry with us.

I don’t see why we shouldn’t make friends.

c) in attributive appositive clauses beginning with “why” after the noun “reason”:

There is no reason why they shouldn’t get on well together.

I don’t see any reason why he shouldn’t be happy.

d) in construction of the following kind:

The door opened and who should come in but Tom.

As I was crossing the street, whom should I meet but Aunt Ann herself.

e) in the set phrase: How should I know?