🗺️ MUST / MUSTN'T GRAMMAR MAP

STRONG OBLIGATION (Must = Personal Requirement)

Used for strong internal obligation or rules created by speaker.

(+) Positive S + must + V(bare)

(-) Negative S + mustn't + V(bare) (PROHIBITION!)

(?) Question Must + S + V(bare)?

STRICT PROHIBITION (Mustn't = DO NOT DO IT!)

Expresses that something is strictly forbidden or dangerous.

(+) Positive You mustn't smoke here, You mustn't cheat

(-) Negative mustn't (must not)

(?) Question Mustn't we park here?

1. Form & Structure

Positive Form (Obligation): Subject + must + V1 → I must study for the exam.
Negative Form (Prohibition): Subject + mustn't + V1 → You mustn't touch this wire! (It is dangerous!)
Deduction (99% Certainty): She has worked all day. She must be exhausted.

Example / Question	Positive / Short Answer	Negative / Short Answer
Must: Obligation (+)	You must stop at red light.	Rule / Law
Mustn't: Prohibition (-)	You mustn't park here.	Strictly FORBIDDEN

2. Key Rules & Formation

Rule	Base / Standard Form	Applied Form
Mustn't vs Don't have to Distinction	MUSTN'T = Forbidden! DON'T HAVE TO = Not necessary (you can if you want). Never confuse them!	You mustn't smoke (forbidden) vs You don't have to pay (free, optional).

State mandatory requirements and safety prohibitions.

mustmustn'tmust notobligationprohibitionforbidden

Prohibition Alert:

Mistake 1: Confusing "mustn't" with "don't have to"
❌ Incorrect: You mustn't pay today, it is free.
✓ Correct: You don't have to pay today, it is free.
Note: Mustn't means forbidden. Don't have to means optional.

No! The past tense of "must" is "had to": "Yesterday I HAD TO study" (NOT "musted").

1. Form & Structure

Forming Must vs Mustn't Sentences

Positive Form (Obligation): Subject + must + V1 → I must study for the exam.

Negative Form (Prohibition): Subject + mustn't + V1 → You mustn't touch this wire! (It is dangerous!)

Deduction (99% Certainty): She has worked all day. She must be exhausted.

Example / Question	Positive / Short Answer	Negative / Short Answer
Must: Obligation (+)	You must stop at red light.	Rule / Law
Mustn't: Prohibition (-)	You mustn't park here.	Strictly FORBIDDEN

2. Key Rules & Formation

Rule	Base / Standard Form	Applied Form
Mustn't vs Don't have to Distinction	MUSTN'T = Forbidden! DON'T HAVE TO = Not necessary (you can if you want). Never confuse them!	You mustn't smoke (forbidden) vs You don't have to pay (free, optional).