Obligation and Necessity

less strong than an obligation, and you have another option.

​necessity

something you are expected to do whether you like or not, and no other option.

​obligation

​must

Formula:
S + must + V₁
Example:
- We must eat before we go.
- All students must participate in study tour.

​Have/has to

Formula:
S + have/has + to + V₁
Example:
- I have to study hard.
- Dara has to finish her work before Sunday.

​should (in future)

Formula:
S + should + V₁
Example:
- You should visit your grandparents.
- I should call my clients soon.

​should (in present)

Formula:
S + should + be + V_ing
Example:
- We should be learning English now.
- She should be cleaning her room right now.

​should (in past)

Formula:
S + should + have + V₃
Example:
- He should have prepared to pack earlier two days ago.
- You should have called me if you need any helps.

- Annabel ought to be here right now.
- The journey ought to take about 2 hours.

​ought to (something happening)

- You ought to listen carefully.
- We ought to leave now.
- Lucy ought to go by herself.

​ought to (obligation)

​had better

1. Advice: It's getting late. You had better go now.

2. Hope: My team had better win tonight.

3. Strong advice: You had better take an umbrella or you will get wet.

​to be + supposed to

1. "it is said": The new John Wick movie is supposed to be excellent.

2. Intended: I'm supposed to shop the supplies on the first of the month.

3. Unfulfilled expectation: Arthur was supposed to visit me last night.