The 3 Types of Modal Verbs

Modal Verbs fall into three different categories based on meaning. As a teacher, it helps to be aware of these categories because they 1) allow for different uses of the same word; 2) dictate how multiple modals can be combined in a verb string; and 3) determine whether defective forms can/should be used (we’ll explain this idea later in case you’re unfamiliar with it).

The coursebooks you use may have topics like “Modals of Permission”, “Modals of Deduction,” etc., which are subtypes within the 3 main categories, or flavors. So if you’re already familiar with those, you’ve got a leg up on this post.


The 3 Flavors

The three categories of modals are Epistemic (relating to speculation), Deontic (relating to ideals or regulations), and Dynamic (relating to performance).


  • Modals of Possibility: can, could, may, might
  • Modals of Deduction: could, may, must
  • Modals of Expectation: shall, should (rarely), will, would


  • Modals of Permission: can, could, may
  • Modals of Obligation: must, shall, should, will (imperative)


  • Modals of Ability: can, could
  • Modals of Habit: might, would


Why This Matters

We won’t go into the intricacies of modal verbs having three flavors in this post, as there’s far too much to cover. But in case you’re wondering how to address what seems like inconsistencies with modals, being aware of the three flavors might help. Here’s just a glimpse.


Take ‘can’ as an example: “Can this really be happening?” (EPISTEMIC); “Can I use the restroom, please?” (DEONTIC); “I can do thirty push-ups.” (DYNAMIC).

These commonly-used words having multiple meanings can be tricky for students to wrap their head around. But the good news is that in most circumstances, only one category is applicable, so you only need to consider one definition for each modal.


We rarely use more than one modal at a time, but you can use two in the same verb string if they’re from different categories. You can use an Epistemic then a Deontic, or you could use an Epistemic then a Dynamic.

I once knew someone who would often say “We might could do that.” That was normal for a Southern U.S. dialect, but more widely we would use a defective form for the second modal in the pair, so instead I would say “We might be able to do that.” Consider other possibilities like “She might need to go there,” or “He must be able to do it on his own.”


Modals are ‘defective’, meaning their form can’t change, which sometimes makes grammar tricky. We sometimes use substitutes that are more grammatically malleable. These substitutes are multi-word modals, most of which start with ‘be’ and almost all of which end with ‘to’. For example, ‘be supposed to’ is the defective form of should, and ‘be going to’ is the defective of will.

Some substitutes depend on the modal flavor.  For instance, ‘be able to’ is the substitute for can/could as dynamic, but ‘be allowed to’ is the substitute for can/could as deontic.

Must has multiple defectives — ‘have to’, ‘have got to’, and ‘need to’ — each of which is an exception since they don’t start with ‘be’. But all three of those defective forms apply to must as Deontic (permission). Must as Epistemic (deduction) curiously has no defective form.


What’s the difference between may and might, between can and could, or between will and would? The answer is … it depends on the flavor.

The second word in each pair is called a ‘preterite’. For Dynamic modals (as well as for non-modal verbs), the ‘preterite’ is simply the past form. But for Epistemic modals, they are hypothetical. And for Deontic modals, they are deferential.


If ever you’re wondering why a modal acts one way in certain instances and a second way in other instances, see which category that word falls into for each case, and hopefully that’ll help answer your question!

Since this article’s publication, we’ve done more research into modal verbs and have come up with a more fleshed-out system for explaining the 3 modals, including why these distinctions matter for educators.  To learn more, check out our Flavors of Modal Verbs grammar topic page, complete with video!

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