Should is a modal auxiliary verb. There is no –s in the third person singular.

• He should be here soon. (NOT He shoulds …)
• You should mend your ways.

Should is followed by an infinitive without to. Questions and negatives are made without do.

• You should go now.
• Should I go now?
• No, you should not.

Note that should is the past equivalent of shall in indirect speech.

• They asked, ‘What shall we do?’
• They asked what they should do.

Uses

To express obligation

Should is often used to talk about duty or obligation. It can also be used to say or ask what the correct or best thing to do is.

• You should tell the truth.
• If you are not feeling well, you should consult a doctor.
• There should be an investigation into the cause of the accident.

Note that should is not as strong as must.

In questions, should is used to ask for advice or instructions.

• It is rather cold here. Should I turn the heating on?
• What should we do now?
• Should I seek his opinion?
• Should we talk to him?

To express probability

Should can express logical probability.

• You should find this grammar book helpful.
• He should be here soon – he left home at six.
• ‘Granny will be staying with us for a couple of months.’ ‘That should be nice.’
• I should be able to beat him.
• Mount Everest should be visible from Tiger Hill if the sky is clear.