Should And Shouldn't - The Modal Verbs

Should is a modal verb. Modal verbs follow these rules:
  • Modal verbs do not take any endings like -s, -ed or -ing (never ‘shoulds’ or ‘shoulded’)
  • Modal verbs are followed by the base form of another verb (should do, should be)
  • Modal verbs make questions by inverting the subject and the modal verb (should you?)
I should do
You should do
He/she/it should do
We should do

They should do

Should is most commonly used for making suggestions and recommendations.
  • You should try the new Vietnamese restaurant!
  • We should leave now so we don’t miss the bus.
  • You shouldn’t wash white clothes with brightly colored clothes.
  • The city should fix these potholes!
In some cases, should can also express a duty or responsibility that isn’t being fulfilled, especially when the structure is should + present continuous.
  • I should be working right now.
    • In other words, I have a duty or obligation to work now, but I’m not doing it.
  • You should be wearin your seatbelt.
    • This is stronger than a recommendation, because wearing a seatbelt in a car is mandatory in many places.
Asking a question
Invert the subject and the modal verb should.
  • Should we bring anything to the party?
  • Should I sign up for a gym membership?
  • When should I submit my assignment?
  • Where should we go for our next vacation?
The negative form
The negative of should is should not or shouldn’t + base form.
  • You shouldn’t eat too much sugar.
Should can also be used to express expectations. In this context, there is no sense of recommendation.
  • The train should be arriving soon.
  • Siji should be home any minute now.
  • The test shouldn’t take longer than an hour.
  • The flight shouldn’t cost more than $400.
The past form
The past form of should is used to express a mistake or missed opportunity. In this context, the past action did not happen, which leads to an attitude of regret or criticism. The past is formed by using should have + past participle.
  • I should have studied for the test (but I didn’t).
    • I didn’t study, and I regret it.
  • Amanda should have told me the event was cancelled.
    • Amanda didn’t tell me that the event was cancelled, and I’m criticizing her for it.
If the past form of should is negative, then an action did happen, which leads to an attitude of regret or criticism.
  • I should not have bought this expensive jacket!
    • I bought an expensive jacket, and I regret it.
  • Julie shouldn’t have told everyone her friend’s secret.
    • Julie told the secret, and the speaker is blaming her for it.
Asking a question
It is possible, although not very common, to ask a question using the past of should. In this case, the speaker is asking for advice about a missed opportunity or possible mistake.
  • Should I have brought a gift to the housewarming party?
It may be more natural to ask the same question in another way:
  • Do you think I should have brought a gift to the housewarming party?
There are a few additional ways that should is used in conversation. In these cases, one word is emphasized. They are underlined in the examples.
  • To express thanks for a gift:
    • You shouldn’t have!
  • To say angrily that you don’t know something and can’t be expected to know:
    • How should I know?
  • To express frustration caused by an unfair situation:
    • Why should he get all the credit?