Summary of Understanding English Modal Auxiliaries
Understanding English Modal Auxiliaries: A Complete Guide
Introduction
Modal verbs are auxiliary verbs that express modality: ability, permission, possibility, probability, deduction, requests, and other shades of meaning. This guide focuses on the general uses of common modal verbs in English (can, could, may, might, must, shall, will, would, need, dare, used to) except for detailed coverage of auxiliary forms, obligations, and the distinctions between WOULD and USED TO (these are covered elsewhere). The material breaks each modal into manageable sections with definitions, examples, comparisons and practical notes for university-level learners.
Definition: Modal verbs are auxiliary verbs that modify the main verb to express modality such as ability, permission, probability, deduction, request, willingness, or habit.
How to read this guide
- Each modal has a short definition box, core uses, clear examples, and practical tips.
- Tables compare closely related modals so you can spot differences quickly.
- At the end there is a concise summary and a list of key points for revision.
CAN / COULD
Definition: CAN expresses ability, permission, and possibility in the present; COULD is its past form and also expresses greater tentativeness or politeness.
Core uses
- Ability: physical or mental skill.
- She can lift the box. He could swim at six months old.
- Permission (informal): asking and granting permission.
- Can I leave for a moment? Sure, you can. Could I leave earlier today? (more polite)
- Perception with a sensory verb: gives an equivalent to continuous perception.
- I think I can hear the sea. Can you see that bird?
- Possibility / doubt in questions and negatives.
- Can that be measles? No, it can’t be.
- Past ability (skill): COULD indicates ability in the past (not the achievement).
- She could ride a bike when she was five.
- Logical past deduction uses perfect infinitives after CAN/COULD.
- He can’t have said that. You could have told me.
Practical tip
- Use to be able to when you need a different tense or to express achievement: She was able to pass the exam.
Table: CAN vs COULD
| Function | CAN | COULD |
|---|---|---|
| Present ability | She can speak Spanish. | — |
| Past ability (skill) | — | She could speak Spanish as a child. |
| Permission (present) | Can I go? | Could I go? (polite) |
| Polite request | — | Could you help me? |
| Tentative possibility | It can happen. | It could happen. |
| Past deduction | He can’t have left. | He could have left. |
💡 Věděli jste?Did you know that when CAN is used with passive infinitives it often translates to possible/able expressions in other languages (e.g. “It can be said” = “Možno to povedať”)?
MAY / MIGHT
Definition: MAY expresses permission and factual possibility; MIGHT expresses weaker possibility, polite requests, or reproach when used with perfect forms.
Core uses
- Permission (formal): May I ask a question? (more formal than can)
- Factual possibility: You may hear the song everywhere.
- Tentative inference (present/future): He may be at the library.
- Past possibility (perfect infinitive): She may have missed the bus.
- Polite/less direct requests: Might I trouble you for the sugar?
- Reproach with MIGHT and perfect infinitive: You might have told me earlier.
Table: MAY vs MIGHT
| Function | MAY | MIGHT |
|---|---|---|
| Permission | May I come in? | — |
| Present/future possibility | She may come. | She might come. (weaker) |
| Past possibility | She may have missed it. | She might have missed it. |
| Politeness | May I? (formal) | Might I? (very polite) |
| Reproach | — | You might have helped. |
💡 Věděli jste?Fun fact: The negative form mayn’t is rare and speakers usually prefer mustn’t to express prohibition.
MUST (deduction) — limited to deduction uses here
Definition: MUST + infinitive is commonly used for strong logical deduction about the present; MUST + perfect infinitive is used for deduction about the past. In negatives, CAN’T is used instead.
Core uses (deduction only)
- Present de
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Modal verbs: general uses
Klíčové pojmy: Modal verbs modify the main verb to express ability, permission, possibility, deduction, willingness and habit., Can expresses present ability, permission and perception; could is past ability or a polite/tentative form., May gives formal permission and factual possibility; might is weaker or used for reproach with perfect infinitive., Must (deduction) forms: must + infinitive for present deduction; must + perfect infinitive for past deduction; negatives use can’t., Shall is mainly formal: 1st-person future, suggestions (Shall we?), and legal usage in 2nd/3rd persons., Will expresses future predictions, willingness, habitual characteristics, and past deduction with perfect infinitive., Would serves as past of will in reported speech, marks past characteristic behaviour, conditionals and polite requests., Need as a semi-modal appears in negatives/questions (needn’t, Need you...); prefer ordinary verb forms in informal speech., Dare functions as marginal modal in negatives/questions and as a full verb with to-infinitive., Used to marks past habitual states; for present habitual actions use simple present.
## Introduction
Modal verbs are auxiliary verbs that express modality: ability, permission, possibility, probability, deduction, requests, and other shades of meaning. This guide focuses on the general uses of common modal verbs in English (can, could, may, might, must, shall, will, would, need, dare, used to) except for detailed coverage of auxiliary forms, obligations, and the distinctions between WOULD and USED TO (these are covered elsewhere). The material breaks each modal into manageable sections with definitions, examples, comparisons and practical notes for university-level learners.
> Definition: Modal verbs are auxiliary verbs that modify the main verb to express modality such as ability, permission, probability, deduction, request, willingness, or habit.
## How to read this guide
- Each modal has a short definition box, core uses, clear examples, and practical tips.
- Tables compare closely related modals so you can spot differences quickly.
- At the end there is a concise summary and a list of key points for revision.
## CAN / COULD
> Definition: CAN expresses ability, permission, and possibility in the present; COULD is its past form and also expresses greater tentativeness or politeness.
Core uses
- Ability: physical or mental skill.
- She can lift the box. He could swim at six months old.
- Permission (informal): asking and granting permission.
- Can I leave for a moment? Sure, you can. Could I leave earlier today? (more polite)
- Perception with a sensory verb: gives an equivalent to continuous perception.
- I think I can hear the sea. Can you see that bird?
- Possibility / doubt in questions and negatives.
- Can that be measles? No, it can’t be.
- Past ability (skill): COULD indicates ability in the past (not the achievement).
- She could ride a bike when she was five.
- Logical past deduction uses perfect infinitives after CAN/COULD.
- He can’t have said that. You could have told me.
Practical tip
- Use to be able to when you need a different tense or to express achievement: She was able to pass the exam.
Table: CAN vs COULD
| Function | CAN | COULD |
|---|---:|---:|
| Present ability | She can speak Spanish. | — |
| Past ability (skill) | — | She could speak Spanish as a child. |
| Permission (present) | Can I go? | Could I go? (polite) |
| Polite request | — | Could you help me? |
| Tentative possibility | It can happen. | It could happen. |
| Past deduction | He can’t have left. | He could have left. |
Did you know that when CAN is used with passive infinitives it often translates to possible/able expressions in other languages (e.g. “It can be said” = “Možno to povedať”)?
## MAY / MIGHT
> Definition: MAY expresses permission and factual possibility; MIGHT expresses weaker possibility, polite requests, or reproach when used with perfect forms.
Core uses
- Permission (formal): May I ask a question? (more formal than can)
- Factual possibility: You may hear the song everywhere.
- Tentative inference (present/future): He may be at the library.
- Past possibility (perfect infinitive): She may have missed the bus.
- Polite/less direct requests: Might I trouble you for the sugar?
- Reproach with MIGHT and perfect infinitive: You might have told me earlier.
Table: MAY vs MIGHT
| Function | MAY | MIGHT |
|---|---:|---:|
| Permission | May I come in? | — |
| Present/future possibility | She may come. | She might come. (weaker) |
| Past possibility | She may have missed it. | She might have missed it. |
| Politeness | May I? (formal) | Might I? (very polite) |
| Reproach | — | You might have helped. |
Fun fact: The negative form mayn’t is rare and speakers usually prefer mustn’t to express prohibition.
## MUST (deduction) — limited to deduction uses here
> Definition: MUST + infinitive is commonly used for strong logical deduction about the present; MUST + perfect infinitive is used for deduction about the past. In negatives, CAN’T is used instead.
Core uses (deduction only)
- Present de