It is said that there are three types of modality: deontic, epistemic and dynamic.

Here are sample sentences for each type of modality:

(1) You can stay as long as you want. [deontic]

(2) You may be right. [epistemic]

(3) He can drive better than you. [dynamic]

The first two names are said to be derived from the Greek for "biding" and "knowledge", respectively.

As far as 'epistemic' is concerned, the meaning derived from the Greek is such that I can easily understand why linguists who coined these terms did so.

As for 'dynamic' and 'deontic', however, it's not as clear to me why 'dynamic' and 'deontic' are chosen to coin the term 'dynamic modality' and 'deontic modality', respectively.

Specifically, what's so 'dynamic' about sentence (3)? (3) represents the subject's ability. I mean, what has being 'dynamic' got to do with anything about the subject's ability?

And what's so 'deontic' about sentence (1)? (1) represents the speaker's permission, and not any sort of 'duty' as expressed by the word 'deontic'.

Hence these questions:

What's the specific meaning of 'dynamic' in 'dynamic modality' that is descriptive of this type of modality?

Why use the difficult word 'deontic' when it doesn't actually represent the whole picture of the type of modality that it's supposed to represent?

  • 1
    The Wikipedia entry for deontic modality attributes "dynamic modality" to F. R. Palmer. I never heard the term. en.wikipedia.org/wiki/Deontic_modality#cite_note-4
    – Greg Lee
    Mar 4, 2015 at 13:45
  • It's also called Alethic; it deals with personal abilities, and it's the only non-deontic reading for can outside a negative environment; epistemic can is an NPI. Alethic only happens with can, not the other diamond modals. Deontic (aka "root") modality and epistemic (aka "logical") modality are standard; "dynamic" is an outlier and very specifically attached to lexical items. Mar 4, 2015 at 20:19
  • For details on Modals, see the Logic Study Guide; there is also a fact sheet on Modality. Mar 4, 2015 at 20:25
  • There is a serious confusion of terms, here, comparing linguists' use and logicians'. According to the latter (and to everyone except linguists, actually), alethic modality concerns possibility and necessity (which linguists call epistemic), and epistemic modality concerns belief and knowledge. Luckily, everyone seems to agree that deontic modality is about permission and obligation.
    – Greg Lee
    Mar 4, 2015 at 22:04
  • 1
    @GregLee Epistemic, deontic and dynamic are the Modal Trinity in Huddleston & Pullum, Cambridge Grammar of the English Language, and Aarts, Oxford Modern English Grammar. Mar 4, 2015 at 23:41

1 Answer 1


Permissive can is 'deontic' because its domain is that of obligation: it conveys a sense of unbinding or absence of obligation. You can stay as long as you want means that you are not 'bound' or 'obliged' to leave at any particular time. This permissive use designates a different kind of possibility than that conferred by physical ability (John can bench-press three hundred pounds) or logical inference (That can't be true!)

The term dynamic derives from a Greek verb whose root meaning is 'be able', 'have the power', so this use is in fact etymologically closer to the original sense than more familiar uses.

Note by the way that there are dozens of 'types' of modality, not just three. These three come to the fore in discussing English modal verbs because they have been found (somewhat) useful for categorizing the distinguishable ranges of meaning and syntactic use each modal exhibits.

  • Permissive can is deontic: She can attend the ball. Ability can is alethic: She can bench-press 200 kg. Negative can't may be either one of these (She can't attend the ball; she can't bench-press 200 kg), or it may be epistemic: This can't be the place. Mar 4, 2015 at 20:22

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