Should gives advice: it's a good idea, but it's the other person's choice: You should see a doctor. Must is stronger: it's necessary: You must see a doctor immediately.
Same situation, two choices. Pick an example.
You should see a doctor about that cough.
A good idea: the other person decides.
You must see a doctor. It looks serious.
No real choice: it needs to happen.
| Rule | Should | Must |
|---|---|---|
| Strength | Advice: a good idea | Necessary: no real choice |
| Who decides | The listener | The speaker or the rules |
| Past | should have + participle (a regret) | had to |
| Example | You should try the cake. | You must arrive by 9. |
It's only a suggestion, but you _____ try yoga.
Paste an email or an essay. Clarigram marks the mistakes you actually make, shows the rule behind each one as a picture, and builds your practice from them.
Yes: The parcel should arrive today means you expect it to. That's should for certainty, on the how-sure gauge.