What Is a Modal Verb?
Modal verbs are auxiliary verbs like can, could, must, and should that add meaning about ability, obligation, or possibility to another verb. English has 10 core modals, each with only one form and no -s, -ing, or -ed endings.
A modal verb is followed directly by the base form of another verb, with no "to" attached. "You must go" works; "you must to go" doesn't. The two exceptions are "ought to" and "have to," which keep the "to" by convention. Full breakdowns of each rule, plus how modals interact with tense, sit at /grammar/ and /grammar/tenses/.
Our query data shows modal verbs draw uneven interest by native language: 21.4% of modal-verb searches come from German speakers, compared to 8.7% from Spanish speakers. German grammar assigns modals a heavier grammatical load through case, mood, and verb-second word order, which may explain why German learners search for pair-by-pair comparisons like can vs could or must vs have to more often than other groups.
If modal verbs still feel unpredictable in context, a short placement check clarifies where you stand. Examinizer's free test takes 25 minutes and covers all CEFR levels from A1 to C2.
Modal Verbs Comparison Table (Can, Must, Should, Will, May and Their Pairs)
| Pair | Difference | CEFR Level |
|---|---|---|
| Can / Could | Present ability vs past ability or polite request | A1-A2 |
| Must / Have to | Subjective obligation vs external obligation | A2-B1 |
| Should / Ought to | Advice; should dominates in everyday speech | B1 |
| Will / Would | Future prediction vs hypothetical situation | B1-B2 |
| May / Might | Possibility; might signals lower probability | B2 |
Can shows present ability ("I can swim"), while could covers past ability or softens a request ("Could you help me?"). Must expresses obligation you impose on yourself, whereas have to signals an external rule, like a workplace policy or a law.
Should and ought to both give advice, but should dominates spoken English. Ought to survives mostly in formal writing and older textbooks. Will predicts future events with confidence ("It will rain tomorrow"), while would shifts into hypothetical territory, a distinction covered in detail on our conditionals page. May and might both express possibility, though might points to a lower chance of something happening.
Want to check your own grasp of these pairs? Examinizer's free test gives an instant CEFR level estimate.
CEFR Level Breakdown: When Modal Verbs Are Taught (A1-C2)
The CEFR framework, developed by the Council of Europe, structures how textbooks introduce modal verbs across six levels. A1 students meet can and can't first, using them only for basic ability. A2 adds could, must, and have to, covering past ability and simple obligation.
B1 brings in should, ought to, and may for advice and possibility, while B2 layers on might, would, and modal perfects such as "must have gone." By this point learners are juggling seven or eight modals with overlapping meanings, which is exactly where things fall apart. C1 and C2 shift focus toward nuanced modal use inside passive and conditional structures, topics covered in detail on our passive voice and conditionals pages.
B1 and B2 introduce more new modal forms in a shorter span than any other stage, which is why intermediate learners often mix up four or five modals at once.
If you're unsure which CEFR level your modal verb knowledge actually sits at, our free test places you in under 25 minutes. A certificate costs €8 (incl. 21% EU VAT = €9.68) and arrives by email within 30 seconds, though it's not a substitute for accredited exams like Cambridge or TOEFL.
Common Mistakes with Modal Verbs
Five errors account for most of the modal verb mistakes in our test data. The most frequent adds "to" after a modal, producing "I can to swim" instead of "I can swim." A close second treats modals like regular verbs and adds "-s" for third person, giving "she cans" instead of "she can." Neither modal ever takes "to" directly or an "-s" ending, regardless of subject.
A large share of B1-level test errors involve confusing "must" (certainty: "she must be tired") with "have to" (external obligation: "I have to finish this by Friday"). Learners also overuse "might" in formal writing where "may" fits better, and many drop modal perfect forms entirely, writing "I should know" when they mean "I should have known" about a past situation.
These five patterns rarely appear in isolation on a real exam. They show up mixed together in reading passages and error-correction tasks, so isolated grammar drills only get you partway there. A full grammar test at /english-grammar-test/ mixes modal questions with the other structures examiners actually test, showing how well you handle them under normal test conditions rather than in a single-topic worksheet.
When to Use Each Modal Verb
Can/could covers three separate meanings depending on context: ability ("I can swim"), permission ("Could I leave early?"), or a polite request. The verb form stays the same; only context signals which meaning applies.
Must signals strong obligation or logical certainty ("You must be tired"), while have to points to an external rule someone else imposed, like a workplace policy or law. Should and ought to both give advice, but should is the far more common choice in spoken English, making it the safer default for exam answers and everyday speech.
Will expresses future facts and promises ("It will rain," "I will call you"), whereas would shifts into hypotheticals and softer, more polite phrasing ("Would you mind?"). May and might both express possibility, but may carries an extra formal-permission sense ("You may leave now") that might doesn't share.
Modals also interact constantly with articles, a pairing broken down at /grammar/articles/. To see where your own modal usage stands, Examinizer's free test gives a CEFR-aligned snapshot in a few minutes, no sign-up required.
Modal Verbs Are Not Just an English Challenge
German's Modalverben system includes six core modals, each with subjunctive forms that shift meaning and formality. Learners carry that complexity into English, where modals like "can," "must," and "should" never conjugate for person or tense. A German speaker expects "können" to change form; English "can" simply doesn't, and that mismatch causes real confusion, one likely reason German speakers generate 21.4% of the modal-verb queries in our data, against 8.7% from Spanish speakers.
Spanish learners face different obstacles, often rooted in mood rather than conjugation, which may explain the lower query volume alongside different error types. Both groups benefit from targeted practice rather than translation exercises that map one grammar system onto another.
Examinizer's free test takes 25 minutes and flags which modal verbs need review before they show up on a CEFR exam.