Uses of Should

Indirect speech
Should is the past tense of shall in indirect speech.

• The officer said, ‘The scoundrel shall be given a good beating.’
• The officer said that the scoundrel should be given a good beating.

Duty and obligation
Should can be used with pronouns of all the three persons to talk about duty and obligation.

• We should help the poor and the needy.
• We should not lie.
• We should all work for the common good.
• You should pay the fees in time.

Conditional clauses
Should can be used in conditional clauses expressing possibilities, suppositions etc.

• If she should come, ask her to wait.
• Should it rain, we will cancel the trip.

Should is often used in main clauses which are preceded or followed by a clause expressing unreal conditions.

• If I were you, I should accept this offer.
• No Sam, I shouldn’t do that, If I were you.

Note that this kind of sentence is often used to give polite advice or gentle admonition.
Possibility
Should is often used to express possibility or likelihood.

• I should be able to finish this work in time.
• You should be able to beat him.

After lest
Should is the only auxiliary verb that can be used after lest.

• Watch and pray lest you should fall into temptation.

Should and shall
Should expresses less possibility than shall.

• I shall be able to meet Peter.
• I should be able to meet Peter.

Here the first sentence expresses a greater possibility of the event – meeting Peter – taking place.

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