should, must, have to
Advice, obligation and prohibition.
The rules
- Advice uses "should" + base verb.
- External rules and laws use "have to" (or "must").
- "Mustn't" = prohibited. "Don't have to" = not necessary (but allowed!).
- No obligation = "don't have to". "Mustn't" would ban paying.
- Modal + base verb: "should drink".
- Strong personal obligation: "must". "Should" is weaker advice.
- Past advice (too late now) uses "should have" + past participle.
Examples
- You should see a doctor about that cough.
- In the UK, you have to drive on the left.
- You mustn't park here.
- The entrance is free, so you don't have to pay.
- You should drink more water.
- I must finish this report tonight, the client presents at 9 am.
- You should have studied harder.
Quick check
Pick an answer to see the rule behind it.
1.You _____ see a doctor about that cough.
2.In the UK, you _____ drive on the left.
3.Which sentence means "it is NOT allowed"?
4.The entrance is free, so you _____ pay.
5.I _____ finish this report tonight, the client presents at 9 am.