Modal Verbs for Prohibition

To say something is prohibited in English, we use the verbs: can’t, mustn’t, may not, not be allowed to.

For example: Staff may not wear casual clothes to work.

                   Staff can’t wear casual clothes to work.

                   Staff mustn’t wear casual clothes to work.

                   Staff are not allowed to wear casual clothes to work.

The table below shows how to use can, be allowed to and may.

	Can	Be allowed to	May
Yes/No Question	Can I smoke here?	Am I allowed to smoke here?	May I smoke here?
Yes/no Answer	Yes, you can. No, you can't	Yes, you are. No, you aren't.	Yes, you may. No, you may not.
Question word question	Where can I smoke?	Where am I allowed to smoke?	Where may I smoke?
Positive Response	You can smoke here.	You are allowed to smoke here.	You may smoke here.
Negative Response	You can’t smoke here.	You aren’t allowed to smoke here.	You may not smoke here.

Must works differently to can, be allowed to and may.

We don’t usually use must in questions. Instead we use: have to.

Do I have to smoke outside? Yes, you do.  No, you don’t.

Where do I have to smoke?

We usually use must in questions to demonstrate annoyance.

Must I smoke outside? (It’s cold and I don’t want to.)

The positive form is: You must smoke outside.

The negative form is: You mustn’t smoke inside.

Click on the links below to learn more about modal verbs

Introduction

Modal Verbs for Ability

Modals for Permission

Modals for Offers and Requests

Modals for Suggestions and Advice

Modal Verbs for Prediction

Modals for deduction and supposition – Present

Modals for deduction and supposition – Past

Modal Verbs for Obligation and Necessity

Past Modals