Should is a modal verb.
After should you use the base form of the infinitive (= verb without to)
Should + Verb (base form of infinitive)
Example: You should go now (do not say: You should to go now.)
When do you use should?
1. To give advice, a recommendation or a suggestion
This is to say that it is the right thing to do or the correct thing.
- Does your tooth still hurt? You should make an appointment with the dentist.
- I think you should study for the test so that you don’t fail.
- Your hair is too long. You should get a haircut.
- You really should go to the new restaurant on Main Street.
2. Expresses that a situation is likely in the present
- Mary should be at home by now. Give her a call.
- He should have the letter by now. I sent it a couple of weeks ago.
3. Expresses that a situation is likely in the future (prediction)
- They should win the game because they are a much better team.
- I posted the cheque yesterday so it should arrive this week.
- It should be fine tomorrow.
4. Expresses an obligation that is not as strong as Must.
Sometimes should is used instead of must to make rules, orders or instructions sound more polite. This may appear more frequently on formal notices or on information sheets.
- On hearing the fire alarm, hotel guests should leave their room immediately.
- Passengers should check in at least 2 hours before departure time.
- You should never lie to your doctor.
- You should pay more attention in class.
- You should be at work before 9.
All of the above example sentences can have must instead of should making the obligation stronger and less polite.
5. Was expected in the past but didn’t happen (should + have + past participle)
This expresses the idea that the subject did not fulfill their obligation in the past or did not act responsibly.
- You should have given your boss the report yesterday when he asked for it.
- I should have studied more but I was too tired.
6. Not fulfilling an obligation (should + be + verb-ing)
This expresses the idea that the subject is not fulfilling their obligation or is not acting sensibly.
- You should be wearing your seatbelt. (The person isn’t wearing one right now)
- We should be studying for the test. (We are not studying right now and we should)
We use shouldn’t to advise not to do something, usually because it is bad or wrong to do.
- You shouldn’t throw your litter onto the street.
- We shouldn’t leave without saying goodbye.
- He shouldn’t play with those wires if he doesn’t know what he is doing.
- Are you tired? You shouldn’t work so much.
- You shouldn’t talk like that to your grandmother.