Modal Auxiliary Verbs Explained (With Everyday Examples)

In the last post, we touched on modal verbs as a special group of auxiliary verbs. They deserve their own deeper look, because they are some of the most misused words in English, not because people don't know them, but because their exact shades of meaning are easy to blur.

So, What Exactly Is a Modal Auxiliary Verb?

A modal auxiliary verb sits before a main verb to add meaning about possibility, permission, ability, obligation, or certainty. The common ones are: can, could, may, might, must, shall, should, will, would.

Here's the important part: modals never change form. You don't say "he cans" or "she musted." They stay exactly as they are, regardless of the subject or tense, which already sets them apart from ordinary verbs.

Breaking Down What Each Modal Actually Signals

Can / Could: Ability and Permission

Can expresses present ability or informal permission: "I can swim." "Can I borrow your pen?" Could is the past form of ability, or a more polite, less certain version of "can": "I could swim when I was six." "Could you help me with this?"

May / Might: Possibility and Formal Permission

May signals possibility or formal permission: "It may rain later." "May I come in?" Might signals a weaker, more uncertain possibility than "may": "It might rain later" suggests less confidence than "It may rain later."

Must: Strong Obligation or Confident Deduction

Must is one of the strictest modals. It can express strong obligation, "You must submit the form by Friday," or a confident logical conclusion, "She's not answering her phone, she must be asleep."

Should: Advice and Expectation

Should is softer than "must." It suggests advice or what is expected, not a strict requirement: "You should see a doctor about that cough." It leaves room for choice in a way "must" doesn't.

Will / Would: Future Certainty and Politeness

Will expresses a decision, promise, or future certainty: "I will call you tomorrow." Would softens requests or describes past habits and hypothetical situations: "Would you mind closing the door?" "When I was young, I would walk to school every day."

The Trap Most Learners Fall Into

The biggest mistake isn't grammatical, it's about tone. Choosing "must" when you mean "should" can sound far harsher than intended. Telling a colleague "You must finish this today" reads as an order, while "You should finish this today" reads as advice or a suggestion. Since both are grammatically correct, the difference lies entirely in how strong you want the statement to feel. This is exactly why modal verbs show up so often in WAEC and JAMB comprehension and lexis questions: examiners are testing whether you understand shades of meaning, not just spelling.

A Simple Practice Exercise

Take a sentence expressing obligation and rewrite it five times, once with each of can, may, must, should, and would. Notice how the meaning shifts each time, even though the rest of the sentence stays identical. "You can leave now" feels neutral. "You must leave now" feels urgent. "You should leave now" feels like advice. That shift is exactly the skill this exercise builds.

Where to Go From Here

Modal verbs work closely with sentence transformation, particularly when converting statements between active and passive voice or between direct and reported speech, since the modal often needs to change form too ("must" becomes "had to" in reported speech, for instance).

For a full breakdown with WAEC and JAMB style practice questions, Akademia's Grammar category covers modal auxiliary verbs in more detail. If you'd like the structural explanation of how modals fit within a sentence, my book Functional & Structural Description of the Sentence in English explores that further.

Next time you write a request, an instruction, or a piece of advice, pause and ask which modal best matches the strength of what you actually mean. It's a small habit that sharpens both your grammar and your tone.