The naughty bus kept on going.
The - determiner
naughty - adjective
bus - noun
kept - auxiliary verb
on - verb particle
going - main verb
That is, 'going' is the main verb, not a gerund.
I see your point and I can partly go along with what you say.
Next I am going to show you why I think it is not:
1. In forming negative finite clauses, not comes after the auxiliary:
It kept not on going. -- ungrammatical
2. Contraction is institutionalized, that is, the contracted form of not is cliticised onto the auxiliary. Let us see whether it works:
It keptn't on going. -- ungrammatical
3. If keep is the first verb in the sentence and is an auxiliary, it follows 'keep' is the operator. Does the subject-operator inversion work?
Kept it on going? -- ungrammatical
Kept on it going? -- ungrammatical
4. operator in reduced clauses:
- Kept it on going?
- Yes, it kept. -- ungrammatical
The bus kept going and so did on the plane. -- ungrammatical
The bus kept going and the plane kept too. -- ungrammatical
- predication fronting:
It was said the bus kept on going and on going it kept. -- ungrammatical
It was said the bus kept on going, which it kept. -- ungrammatical
5. Pre-adverb position
frequency subjunct like never usually precedes the main verb but follows the auxiliary:
It kept never on going. -- ungrammatical
It kept on never going. -- ungrammatical
It never kept on going. -- correct
'kept' smells like a main verb here.
6. Quantifier position
They will all go. -- correct
They all kept on going. -- correct
They kept all on going. -- ungrammatical
7. Independence of subject
It kept on going. -- correct
He kept on going. -- correct -- semantical independence from the subject (both he and it works)
There will be peace. -- correct
There kept on going. -- ungrammatical
8. Most importantly, auxiliaries do not inflect for person and tense.
He wills -- ungrammatical
He keeps -- correct
As you can see, 'keep' fails all the tests for auxiliaries. However, it does no follow that 'keep' in the sentence is a true-blue main verb. You probably know that there is a gradience running through the class of main verbs and auxiliaries. There are verb constructions that are neither fish nor fowl, that is, they have an intermediate status on a gradient between auxiliaries at one end and main verbs on the other. Where is 'keep on' on this scale. That is our task to pinpoint. The battle lines are drawn. Let us proceed at full pelt ahead.
What I am trying to do next is prove that 'keep' and 'on' belong together. Why? Because I think I can prove hands down that 'keep on' cannot occur in any one sentence as the only constituent that even remotely resembles a verb.
'keep on' belongs together:
It [kept on] going.
It [continued] going.
If on is not attached to 'kept', it means it enjoys relative freedom regarding where it sits in the sentence.
Adverbials can take place between any two constituents that are immediatelly controlled by the S node (x-bar syntax).
It kept going on ≠ It kept on going.
In light of the phenomena we have just witnessed here, I have no choice but to yield to the idea that 'keep on' is one.
If it is one, it is the main verb here:
I kept on. :cross:
Because it is :cross:, I am forced to think it is not a main verb. What is it then? It is floating in mid-air. What are called those classes that float somewhere with regard to their verb class statuses?
1. marginal modals
2. modal idioms
keep on = 1?
keep on = 2?
keep on = 3?
keep on = 4?
What is a marginal modal? What is it? 'used to', ought to', dare', need'.
I keptn't on going. :cross:
Did I keep on going? :tick:
I usedn't smoking? :tick:
I did not used to smoke. :tick:
They behave differently --> no marginal modal.
2. modal idioms: combination auxiliary
plus to or adverb -- 'keep on' does not belong here, either.
3. semi-auxiliaries: introduced by 'be' or 'have' -- keep on is not on of them
By process of elimination, we have arrived at the class of catenatives. If 'keep on' were not a catenative, it would belong nowhere, which we no is not true. So, 'keep on' must be a catenative.
What are catenatives? They are the closest group to main verbs amoung the four groups I have listed above.
'keep on' has meaning related to aspect or modality (just like catenatives and main verbs
It kept on going.
He kept on going. -- the semantics of the verb is independent from the subject (just like in the case of catenatives and auxiliaries
Unlike main verb constructions like expect (to), want (to) and attempt (to), catenative verbs are in no way related to the transitive verb construction, in which the verb is followed by a direct object or prepositional object.
He attempted to attack the burglar. = He attempted an attack.
He kept on attacking the burglar. ≠ He kept it on. :?:
substitute for the aspect auxiliary 'be':
He keep on going = (more or less) He is going.