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

Structure of should

The basic structure for should is:

subject + auxiliary verb
+ main verb

Note that:

Look at the basic structure again, with positive, negative and question sentences:

  subject auxiliary
not main verb
+ He should   work.
- You should not go.
? Should we   help?

Note that the main verb is sometimes in the form:

The main verb can never be the to-infinitive. We cannot say: He should to go.
There is no short form for should, but we can shorten the negative should not to shouldn't.

Use of should

should for advice, opinions

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

People often say "They sthg." Usually, the "they" is anonymous and means the government, or the company, or somebody else - but not us! Here are some examples:

  • They should fix this road.
  • They should have more staff in this shop.
  • They should have abolished this tax years ago.

should for 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:

should for probability, expectation

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

should for conditionals

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

This is not a very important distinction. (More about the use of shall/will and should/would.)

should for If I were you I should...

We often use the conditional structure "If I were you I should..." to give advice.

Note that we can omit "If I were you..." and just say:

In these cases, the phrase "I should" really means something like "you should".

should for pseudo subjunctive

We often use a special verb form called the subjunctive when talking about events that somebody wants to happen, hopes will happen or imagines happening, for example:

However, this is much more common in American English. British English speakers often convey the same idea using should:

Here are some more examples:

typically American English
using should
typically British English
The president is insisting that pollution be reduced. The president is insisting that pollution should be reduced.
The manager recommended that Mary join the company. The manager recommended that Mary should join the company.
It is essential that we decide today. It is essential that we should decide today.
It was necessary that everyone arrive on time. It was necessary that everyone should arrive on time.

should for Why should..?

If we don't understand (or agree with) something, we may use Why should..?, like this:

Why should..? and How should..? can also indicate anger or irritation: