Why there are only 5 modal verbs in English

Question

Modal is a type of auxiliary verb. The complete list of them are:

Can/could/be able to
May/might
Shall/should
Must/have to
Will/would

Another (unnamed?) category of verbs is these 3:

Have
Be
Do

All other verbs are your normal "actions" and are used by themselves as far as I can tell (i.e. "I read the book", just one verb).

My question's first part is, is this all of the modal/helper verbs? Are there any more? What is the complete list?

The main part of the question though is, why these are considered verbs in the first place. Here's why I'm asking that.

(1) I might go to the store.
(2) ~~I possibly go to the store.~~
(3) I might possibly go to the store.
(4) ~~I should could go to the store.~~
(5) I should have used to be going to the store.

So (1) is saying "possibly go to the store" basically. But you can't use "possibly" as a verb (2). It is an adverb it looks like (3).

Then, (4), you can't do either. But technically if you break down the meaning, it is a valid thing to say, saying essentially "I should go to the store and I could go to the store.".

Number (5) is just to show this is the max number of verbs I can seem to cram into a sequence.

Why do only these 5 or 8 verbs allow for this direct composition? Why aren't there 100's that have this same feature? What is so special about these?

In my head, I have quite a hard time visualizing these 5 as "actions". It is hard to visualize "may" as an action. Or "should" as an action. So why are they considered actions?

Are there any other areas of research that treats these in novel ways, provides different perspectives, etc.?

Why are there only five? Because if there were more, these five wouldn't be as special. But seriously, English isn't particularly logical, and I'm not sure that there aren't others. Your fifth example sentence doesn't sound quite right to me, I would say "I should have been used to going to the store" (though I'm not certain that that's what you meant). — nnnnnn, Jan 25 '20 at 03:02
It is like why are there only 26 letters in English alphabet! That is how English is. Trying to answer the question of OP, will, would, shall, should, may, might, can, could, must, ought to, dare, (...?) are considered auxiliary verbs. Some people treat will & would, as present and past tenses, whereas some others treat them as separate. Also, review the correctness of the last two sentences OP has mentioned as examples. — Ram Pillai, Jan 25 '20 at 05:17
Does this answer your question? Modal vs Non-Modal vs Auxiliary modal vs Conjugated Verb (Question 1) Also how dare you, how do you dare (especially J Lawler's answer). — Edwin Ashworth, Jan 25 '20 at 12:36

score 0 · Answer 1 · answered Jan 25 '20 at 06:44

I have a partial answer to your second question. I don't know why there should be so few finite auxiliaries (will, must, may, ...), but I do have a theory about why there should be so few kinds of preverbal modifiers in English. The governing grammatical principle comes from Relational Grammar, which has a category of "term relations" with members: 1 (subjects), 2 (direct objects), 3 (indirect objects), Chomeur (former 1,2,3). To which I think must be added a term relation 0 for the performatives (vocative). That makes 5 in all, so that is the maximum of different types of auxiliary in English.

0 : inverted 1's (in questions, e.g.)
1 : finite ("is", "has", modals)
2 : chomeur ("have" substituting for Past, e.g. "may have")
3 : progressive "be" with -ing
4 : passive

Why there are only 5 modal verbs in English

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