Introduction: The Power of Necessity
Welcome to the world of MUST. In English, this small word carries a lot of weight. It is a Modal Verb, which means it helps other verbs express specific moods like necessity, certainty, or rules.
Use this dashboard to explore the three distinct personalities of "Must," visualize how it works in detective stories, and master the tricky past tense changes.
Obligation
"I must study."
Prohibition
"You mustn't smoke."
Deduction
"It must be true."
1. The Three Personalities of MUST
Click a tab below to unlock the rules and nuances for each use case.
Internal Necessity
We use MUST when the speaker feels it is necessary. It is personal. It comes from inside you.
- ✅ "I must call my mom today." (I feel it is important).
- ✅ "We must get together for lunch soon!" (A strong recommendation).
VS. HAVE TO
Use "Have to" for external rules (laws, boss's orders).
"I have to wear a uniform." (Not my choice).
Who is the Boss?
"I MUST do it."
Because I think it's important.
Absolute Prohibition
MUSTN'T (Must not) is not just a suggestion. It means Don't do it! It is forbidden.
Subject + MUST NOT + Verb (base form)
- 📵 "You mustn't use your phone in class."
- 🏎️ "We mustn't drive fast here."
The Detective's Tool
Use MUST when you don't know the facts 100%, but you are very sure based on logic or evidence.
Present Deduction
"His lights are on. He must be home."
(95% Certainty)
Past Deduction
"The street is wet. It must have rained last night."
(Must + Have + Past Participle)
The Certainty Scale
How sure are you?
2. Time Travel: The Past Tense Trap ⏳
"Must" is a stubborn verb. It doesn't like to change form. When we talk about obligation in the past, "Must" disappears and we have to borrow from "Have to".
"I had to work late yesterday."
"I must finish this now."
"I will have to go tomorrow."
3. Test Your Knowledge 📝
1. It's a hospital rule. You ________ smoke inside.
2. Look at those fancy cars! They ________ be very rich.
3. Yesterday, I ________ go to the dentist.