Unit 3: Modals

I. Orientation

Modal verbs are auxiliary verbs that express meanings such as ability, permission, possibility, obligation, advice, prediction, and willingness. They do not usually describe an action by themselves; instead, they modify the meaning of a main verb. In English, the central modal auxiliaries are can, could, may, might, must, shall, should, will, and would. Related semi-modals include ought to, have to, need to, and be able to.

• Governing principle: A modal combines with a main verb to show the speaker’s attitude toward an event.
  • She can drive expresses ability.
  • She must drive expresses necessity or strong obligation.
• Basic structure: A modal is normally followed by the base form of the verb.
  • They may arrive soon.
• Auxiliary function: Modals form negatives and questions without using do.
  • He cannot swim. / Can he swim?
• Meaning depends on context: Must can express obligation (You must submit the form) or logical deduction (She must be at home).
• No ordinary tense system: Most modals do not take -s, -ed, or -ing forms.
  • Correct: He can speak.
  • Incorrect: He cans speak.
• Formal and informal variation: May is often more formal than can for permission, while have to is common in everyday speech for necessity.

II. Rules of Modal Verbs — Form and grammatical behaviour

A. Definition and basic pattern

A modal verb is an auxiliary that precedes a base-form verb and adds a particular meaning such as possibility or obligation. The most common affirmative pattern is:

Subject + modal + base verb + complement

• Subject: The person or thing performing the action.
  • The students can understand the lesson.
• Modal: The auxiliary expressing attitude or force.
  • can expresses ability or possibility.
• Base verb: The unchanged form of the lexical verb.
  • understand, not understands or understanding.
• Example: Rina should revise her notes.
  • should is the modal; revise is the base verb; her notes is the complement.

B. Rules of modal verbs

The rules of modal verbs control their position, form, and combination with other verbs.

• Base verb after a modal: Use the infinitive without to after the central modals.
  • Correct: You must leave now.
  • Incorrect: You must to leave now.
• No subject–verb agreement: A modal remains unchanged with third-person singular subjects.
  • He can play is correct, not He cans play.
  • She will attend is correct, not She wills attend.
• No do-support: Use the modal itself to form questions and negatives.
  • Question: Should we begin?
  • Negative: We should not begin.
  • Not: Do we should begin?
• Modal plus be: A modal can be followed by be to describe a state or a passive construction.
  • State: The room may be quiet.
  • Passive: The report must be submitted.
• Modal plus have: Modal + have + past participle refers to a past possibility, deduction, criticism, or unrealized action.
  • She may have missed the bus.
  • You should have called earlier.
• Modal plus continuous form: Modal + be + -ing describes an action in progress.
  • They might be waiting outside.
• One central modal at a time: Central modals do not normally occur together.
  • Incorrect: He will can come.
  • Correct: He will be able to come.
• Semi-modal alternatives: Use have to, be able to, or be allowed to when a required form is unavailable.
  • She has to work supplies a third-person necessity form.
  • They will be able to attend supplies a future ability form.
• Negative contractions: Cannot is generally written as one word; can’t, shouldn’t, and won’t are contractions.
  • Formal: You must not enter.
  • Informal: You mustn’t enter.

C. Rules for questions and negatives

Questions place the modal before the subject, while negative statements place not immediately after the modal.

• Yes/no questions: Use modal + subject + base verb.
  • Can you solve this problem?
  • May I use your dictionary?
• Wh-questions: Place the question word before the modal.
  • When will the meeting start?
  • Why should they apologise?
• Negative forms: Add not after the modal.
  • He might not agree.
  • You should not ignore the warning.
• Meaning of must not: Must not expresses prohibition, not lack of necessity.
  • You must not touch the switch means “It is prohibited.”
  • You need not touch the switch means “It is unnecessary.”
• Tag questions: The same modal is usually repeated in the tag.
  • She can drive, can’t she?
  • They should leave, shouldn’t they?

III. Usage of Modal Verbs in Syntactical Structures — Meaning and sentence patterns

A. Definition and communicative function

The usage of modal verbs in syntactical structures concerns how modals operate in affirmative, negative, interrogative, passive, perfect, and conditional sentences. Their meaning is determined by both the modal and the structure surrounding it.

• Semantic function: A modal changes the force of the proposition.
  • He is coming states an event.
  • He may be coming presents it as possible.
• Syntactic position: The modal appears before the main verb or before be and have in expanded structures.
• Scope of meaning: The modal generally affects the whole proposition.
  • You must complete the form makes completion obligatory.
• Politeness and interpersonal meaning: Modals soften requests and advice.
  • Could you open the window? is less direct than Open the window.

B. Rules of modal verbs

Modal meanings can be grouped according to the kind of judgment or relationship expressed in a sentence.

• Ability: Can expresses present or general ability; could often expresses past ability.
  • Maya can type quickly.
  • Maya could type at six.
• Permission: Can is common in informal speech, while may is more formal.
  • Informal: Can I leave early?
  • Formal: May I leave early?
• Possibility: May, might, and could indicate that an event is possible.
  • The parcel might arrive tomorrow.
  • Could does not necessarily mean past time in this use.
• Obligation and necessity: Must expresses strong obligation; have to often expresses an external requirement.
  • You must wear a helmet presents a strong instruction.
  • Employees have to display identification may refer to a workplace rule.
• Advice: Should and ought to recommend an action.
  • You should back up your files.
• Prediction and willingness: Will expresses prediction, intention, or willingness.
  • The results will be announced on Friday.
  • I will help you with the equipment.
• Past criticism or unrealized duty: Should have + past participle refers to an action that was advisable but did not occur.
  • You should have checked the address.

C. Usage of modal verbs in syntactical structures

The following structures show how modals combine with different verb forms to express time, aspect, voice, and conditional meaning.

• Affirmative structure: Use subject + modal + base verb.
  • The committee may approve the proposal.
  • may marks possibility; approve remains in the base form.
• Negative structure: Use subject + modal + not + base verb.
  • The committee may not approve the proposal.
  • The sentence denies certainty about approval, rather than necessarily prohibiting it.
• Interrogative structure: Use modal + subject + base verb.
  • May the committee approve the proposal?
  • The modal moves before the subject; do is not added.
• Perfect modal structure: Use modal + have + past participle for a past interpretation.
  • The committee may have approved the proposal.
  • have is the perfect auxiliary; approved is the past participle.
• Perfect negative structure: Place not after the modal.
  • The committee may not have approved the proposal.
  • This means approval is uncertain or is believed not to have occurred, depending on context.
• Continuous structure: Use modal + be + present participle.
  • The committee may be discussing the proposal.
  • be discussing presents the activity as ongoing.
• Perfect continuous structure: Use modal + have been + present participle.
  • The committee may have been discussing the proposal for an hour.
  • for an hour identifies duration; have been discussing links the ongoing activity to the past.
• Passive structure: Use modal + be + past participle.
  • The proposal must be approved by Friday.
  • The proposal receives the action; approved is the past participle.
• Perfect passive structure: Use modal + have been + past participle.
  • The proposal should have been approved yesterday.
  • This expresses an expected past passive action that apparently did not happen.
• Conditional structure: Modals frequently occur in if-clauses and result clauses.
  • If you study regularly, you can improve your pronunciation.
  • If I had more time, I would join the course.
  • would marks the imagined result; had places the condition in an unreal present situation.

D. Contrastive meanings and limitations

Modal choice must match the intended degree of certainty, obligation, time, and formality.

• Possibility versus certainty:
  • She may be in the library means the speaker considers it possible.
  • She must be in the library means the speaker makes a strong deduction from evidence.
• Prohibition versus absence of necessity:
  • You must not disclose the password prohibits disclosure.
  • You do not have to disclose the password says disclosure is unnecessary.
• Past ability versus successful past action:
  • He could swim when he was five describes general past ability.
  • He was able to swim across the river emphasizes success in one particular situation.
• Will versus would:
  • Will you attend the seminar? asks about a future event or willingness.
  • Would you attend the seminar? is more tentative or conditional.
• May versus might: Both express possibility, but might often presents a weaker or more tentative possibility.
  • The train may be delayed suggests a reasonable possibility.
  • The train might be delayed sounds more uncertain.
• Formal restrictions: Central modals cannot normally carry all tense or agreement forms.
  • Instead of He musted leave, use He had to leave.
  • Instead of She cans attend tomorrow, use She will be able to attend tomorrow.
• Contextual interpretation: The same modal may express different meanings.
  • You must be tired is a deduction.
  • You must finish today is an obligation.
• Register: Could you explain this? is a polite request, whereas Can you explain this? is more direct but still acceptable in ordinary conversation.