Understanding how to communicate rules, permissions, and obligations is essential for anyone learning English. Modal verbs combined with passive infinitives form one of the most practical structures for expressing regulations in everyday contexts, from signs in public spaces to workplace policies. Mastering this structure allows you to sound natural and precise when giving instructions or describing what is allowed, required, or prohibited.

What are modal verbs and what functions do they express?

Modal verbs are auxiliary verbs used to express specific functions in English [0:18]. These functions include:

• Permission: indicating what is allowed.
• Ability: expressing what someone can do.
• Obligation: communicating what is mandatory.
• Prohibition: stating what is not permitted.
• Lack of necessity: showing something is not required.
• Advice: recommending a course of action.
• Possibility and probability: suggesting something may happen.

The most common modal verbs for these purposes are could, should, might, may, must, will, and ought to [0:38]. Each one carries a different degree of strength or formality, so choosing the right modal is key to conveying the exact meaning you intend.

How do passive infinitives work with modal verbs?

When modal verbs are paired with a passive infinitive, the structure follows a clear pattern: modal + be + past participle. Notice that in these constructions, the word "to" is not used [1:28]. This is an important difference compared to other passive infinitive forms studied in previous lessons.

Here are some examples that illustrate this pattern [1:02]:

• The door must be locked at all times. — This expresses obligation; it is mandatory to lock the door.
• Pots should be rinsed before cooking. — This gives advice or a recommendation.
• Tickets may be bought after the show starts. — This expresses permission or possibility.
• Reservations can be made three days prior. — This indicates ability or availability.

The subject in each sentence receives the action rather than performing it, which is precisely what makes the construction passive.

What do real-world rules look like with this structure?

Applying modals and passive infinitives to everyday signs and regulations makes the learning concrete. Consider these practical examples discussed throughout the lesson:

How do we express prohibition?

When something is not permitted, you combine the modal with not and the passive infinitive. For instance, "Phones may not be used" [1:56] communicates a clear prohibition, just like a crossed-out cellphone sign you might see in a hospital or theater. Similarly, "Weapon carry will not be permitted" [3:08] uses will not to state a firm rule.

How do we express obligation and advice?

Obligation often uses must, as in "Masks must be worn to enter" [2:20]. This leaves no room for choice — it is a requirement. For advice or strong recommendations, should is the appropriate modal: "Car speed should be reduced to avoid accidents" [2:43] suggests a safer course of action without making it an absolute command.

How do we use "ought to" in passive constructions?

The modal ought to is unique because it does include the word "to" as part of the modal itself. An example from the lesson is "Trash ought to be thrown in the bin" [3:42]. This structure expresses a recommendation or expectation about proper behavior, and it is slightly more formal than should.

These examples show how a single grammatical pattern can cover a wide range of meanings depending on which modal verb you select. The stronger the modal, the less optional the action becomes — from gentle advice with should and ought to, through permission with may and can, all the way to firm obligation with must and prohibition with will not or may not.

Now it is your turn to practice. Think about the rules and regulations that should be implemented at a university dormitory [3:56]. What would be mandatory? What would you recommend? What should be prohibited? Share your ideas using modals and passive infinitives in the comments below.