Are modal verbs, such as must and can, considered lexical or grammatical categories?

  • This is an understated and misunderstood part of grammar. Yes, verb auxiliary is a grammatical function. And lots of words other than the basic uninflected modals can have auxiliary function with various different lexical meanings.
    – William
    Commented Sep 28, 2016 at 19:53
  • @William - but not all auxiliary verbs were created equal. If I say "you will go", "will" is an auxiliary verb, but it is merely inflecting the tense of "go". If I say "you can go", "can" is an auxiliary, but it is not inflecting tense, it is changing the meaning of the whole sentence. Commented Sep 29, 2016 at 10:46

4 Answers 4


I think I must be interpreting the question differently from Greg Lee, because my answer is that (at least in English) they must be a grammatical category, because they are different in syntax from other verbs. Of course the individual modals are defined lexically, but what allows us to use a collective term like "modal verb" is grammatical.

  • Indeed. It has been argued that at least two of the English modals, will and can do not in their primary senses express mood/modality at all. Commented Apr 14, 2016 at 12:15
  • Unaccusative verbs show different syntactic properties to unergative verbs, but we still classify them both as "verbs". Do you mean that modals and lexical verbs are not in complementary distribution?
    – P Elliott
    Commented Apr 16, 2016 at 23:11
  • @ StoneyB they don't have similar semantic meaning at all. They go in front of bare infinitive verbs, changing the meaning of the main/lexical verb in their own way. There are lots of words and phrases that can have auxiliary function.
    – William
    Commented Sep 28, 2016 at 20:03

Historically, the typical modals form a grammatical category known as Präteritopräsentia: They have past tense form, but present tense meaning. Even in Modern English the lack of an -s ending in the third person singular is a remainder of this inheritance. The verb "will" is historically in a category of its own, but joined the other modals in the Germanic languages.


The words themselves are of course not categories. They are however commonly considered to be the conventional grammaticalised means of conveying those categories. Many of them however have multiple senses, and they do not all convey modality in every sense.

  • If you disagree with my answer, please leave a comment so that I can know why and possibly clarify or improve it :)
    – curiousdannii
    Commented Sep 28, 2016 at 12:50

The lexicon contains unpredictable information about words, and since there is no way to tell by examining the pronunciations of "will", "may", and so on that they are modal auxiliaries, then this information must be lexical.

  • This of course holds for every expression, so you're saying that there's nothing substantive to the (often assumed) distinction between lexical and functional items? I happen to agree with this view, incidentally.
    – P Elliott
    Commented Apr 16, 2016 at 23:09
  • You are saying that no information about any expression is predictable? No, I certainly can't agree with that. I don't know what a "functional item" is.
    – Greg Lee
    Commented Apr 17, 2016 at 14:26

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