Modal verbs should and must?

"Should" and "must" are both modal verbs that express different levels of necessity or obligation.

- "Should" is used to indicate a recommendation or a suggestion. It suggests that something is a good idea or the right thing to do, but it is not mandatory. For example, "You should eat more fruits and vegetables for better health."

- "Must" is used to indicate a strong necessity or obligation. It implies that something is required or essential. For example, "You must wear a seatbelt while driving."

Should

- Expresses advice, suggestion, or recommendation:
- You should see a doctor.
- You should eat healthy foods.

- Indicates expectation or obligation (less strong than "must"):
- You should be polite to your elders.
- It should rain tomorrow.

- Expresses probability:
- He should be at home now.
- It should be a great movie.

Must

- Expresses strong necessity, obligation, or prohibition:
- You must submit your report by tomorrow.
- You must not cheat on the exam.

- Indicates logical consequence or certainty (based on evidence or deduction):
- If you touch the fire, you must get burned.
- The sky must be blue.

Key Differences

| Feature | Should | Must |
|---|---|---|
| Strength of obligation | Less strong | Strong |
| Expresses advice | Yes | No |
| Indicates expectation | Yes | Not as strongly |
| Expresses probability | Yes | No |
| Logical consequence | Not usually | Yes |
| Prohibition | Can be used as "must not" | Yes |