English grammar
Modal Verbs
Modal verbs express what is possible, necessary, certain, or permitted. English uses can, could, should, must, might, may and their combinations to cover a huge range of meaning, from simple ability to past regret.
Textbook Modal Verbs
The standard forms taught in English courses worldwide, illustrated with real clips from native speakers, not invented examples.
Ability & Permission
can / could / may + base verb
"Can" and "could" express ability or permission, present and past. "May" is more formal. "Could you help me?" sounds politer than "Can you help me?", a distinction native speakers use instinctively.
Obligation & Advice
must / should / have to + base verb
"Must" and "have to" express strong obligation, with a key difference: "must" usually comes from the speaker, "have to" from an outside rule. "Should" gives advice or a recommendation. Getting this right is essential for sounding natural and appropriate in English.
Possibility & Deduction
must / might / may / could / can't + base verb
These modals form a certainty spectrum. "It must be true" (almost certain), "it might be him" (possible), "she can't be right" (almost impossible). The same verbs that express ability and obligation also express how certain we are, and context tells us which.
Past Modals
should / could / might / may / must + have + past participle
"I must have lost it" (past deduction), "she could have called" (unrealised possibility), "they might have already left" (past speculation), "it shouldn't have been done" (criticism). In natural speech, "have" almost always contracts to 've, "should've", "could've", "must've", and sounds so close to "of" that even native writers sometimes misspell it as "should of". Past modals are one of the hardest areas for learners, and one of the most common in natural conversation.