SHOULD

Should is an auxiliary verb, a modal auxiliary verb. We use should mainly to:

• give advice or make recommendations
• talk about obligation
• talk about probability and expectation 
• express the conditional mood
• replace a subjunctive structure

Structure of Should

subject + should + main verb

The main verb is always the bare infinitive (infinitive without "to").

	subject	auxiliary verb	main verb
+	He	should	go.
-	He	should not	go.
		shouldn't
?	Should	he	go?

Use of Should

should: Giving advice, opinions

We often use should when offering advice or opinions (similar to ought to):

• You should see the new James Bond movie. It's great!
• You should try to lose weight.
• John should get a haircut.
• He shouldn't smoke. And he should stop drinking too

The difference between advice and opinion or suggestion is that an advice is more directly than a suggestion this is general.

should: Obligation, duty, correctness

Another use of should (also similar to ought to) is to indicate a kind of obligation, duty or correctness, often when criticizing another person:

• You should be wearing your seat belt. (obligation)
• I should be at work now. (duty)
• He should have been more careful. 

should: Probability, expectation

We use should to indicate that we think something is probable (we expect it to happen):

• Are you ready? The train should be here soon.
• $10 is enough. It shouldn't cost more than that.
• Let's call Mary. She should have finished work by now.

should: Conditionals

We sometimes use should (instead of would) for the first person singular (I) and first person plural (we) of some conditionals:

• If I lost my job I should have no money.
  (If he lost his job he would have no money.)
• We should be grateful if you could send us your latest catalogue