When does a gerund become a verb?

My question is a follow-up to one in which I identified stealing and killing in a particular sentence as gerunds. Bill J commented to the effect that if objects followed these gerunds, the latter became verbs.

My questions are why and what form of the verb? For me the grammatical distinction between “I dislike killing” and “I dislike killing sheep” is simply that the gerund complement in the first becomes a gerund phrase complement in the second.

Running as a noun, a verb, or an adjective

ᴛʟᴅʀ: Not all -ing words in English are gerunds; some -ing words are not gerunds at all but rather nouns or adjectives. Therefore gerunds never “become” verbs because they never are not verbs. Gerunds are always verbs. However, gerund phrases can be used where a noun phrase is called for.

A. Running as a deverbal noun

If an -ing word takes determiners and plural inflections and adjectives and adjectival prepositional phrases, it must be a noun not a verb. These are deverbal nouns, not gerunds. They resist adverbs and verbal complements like direct or indirect object.

The annual running of the bulls during Pamplona’s San Fermín festival is fraught with peril.
How many bull runnings take place across Spain and Portugal every summer?

In sentence 1, running takes the determiner the, the adjective annual, and the prepositional phrase of the bulls. It is clearly a noun, not a verb.

In sentence 2, runnings is the plural noun inflection, so it is again clearly a noun, not a verb.

So whether it’s this or that running or these or those runnings, these guys are always merely nouns. They are not gerunds because they are not verbs. That’s why we call them deverbal nouns, because although they long ago began life as verbs, they’ve since been defrocked, so to speak, and so now are but common nouns only.

B. Running as a verb: the gerund

In contrast, if an -ing word takes object complements and adverbs and adverbial prepositional phrases but resists those other things mentioned, then it must be a verb not a noun. These are the ones people call gerunds. A gerund is a verbal inflection used for a particular kind of non-finite verbal phrase; it acts mostly like a to-infinitive phrase does in this regard.

Like a to-infinitive, the entire gerund phrase serves as a noun phrase and so can serve as the subject of a clause or the object of a preposition, but the gerund itself is a verb form that does verb things.

Running bulls is harder work than herding cats.
The local custom of wildly running unchaperoned bulls through the streets of Pamplona has attracted countless tourists over the years, and injured not a few.
Running scared is sometimes preferable to standing still.

Notice how in sentence 3, the subject running bulls takes the singular verb is. That shows that bulls is not the subject and that running is not an adjective. Running is a verb and bulls that verb’s complement, and a gerund phrase is always considered singular for purposes of verbal concordance.

Sentence 4 demonstrates using the adverb wildly on running, again proving it a verb here.

Sentence 5 might mislead you into thinking running and standing are nouns because scared and still are adjectives. However, these are actually verbs whose complements are adjectives here.

C. Running as a participial adjective

An -ing word can also act as a participial adjective. It acts as an adjective now, not as a verb.

Loudly running bulls are more perilous than quietly sleeping ones.
Loud, running bulls are more noticeable than quiet, sleeping ones.

Notice how in both 6 and 7, running bulls takes a plural verb, are. That shows you that running is merely an adjective here. Notice how it precedes its noun just like any other normal adjective does in English.

We can use the adverb loudly to modify the adjective running as in 6. But in 7 we use the adjective loud so it modifies not running but bulls; hence the comma.

D. Running as a verb, revisited: the (present, active) participle

Lastly, an -ing word can be an actual participle, which like the gerund is a non-finite form of the verb. It can therefore serve as the head of a participle phrase. These participle phrases can modify either nouns or verbs, or serve as absolutes that apply to the entire sentence.

The person running bulls through the streets had best be fleet of foot.
I really tired myself out running bulls through the streets yesterday.
Running bulls through the streets yesterday, I really tired myself out.

In cases like example 8, this sort of right-branching modifying phrase of a noun can be seen as an instance of whiz-deletion, with something like who is considered to have gone missing.

The person (who is) running bulls through the streets had best be fleet of foot.
The person (who will be) running bulls through the streets had best be fleet of foot.
The person (who goes) running bulls through the streets had best be fleet of foot.

In example 9, the participle phrase is an adverbial of manner; it modifies the verb phrase tired myself how. In 10 it is an absolute participle phrase that applies to the entire sentence.

You can also think of these adverbials as being the secret objects of deleted prepositions:

I really tired myself out (by) running bulls through the streets yesterday.

Oh no! Caveat Lector

Wait, did you see that? We just changed our analysis of running where it’s a verb acting adjectivally (so a participle) to a verb acting nominally (so a gerund).

Which one is it really?

The answer is that it doesn’t matter. It’s just an -ing word. The lessons here is that you shouldn’t get so hung up on applying Latin terms to English. Some linguists call these words gerund–participles recognizing that the boundaries aren’t so clear cut in English the way they are in Latin.

Using Latin words like gerund and participle for English -ing words isn’t especially useful, and can be genuinely confusing. The various jobs that our -ing words do for us are easier to understand if you avoid confusing terminology from a borrowed language now long dead.

Resolving Ambiguity

Your original question attempts to figure out whether an -ing word is acting like a noun or a verb. You do have a point that there is ambiguity inherent in a phrase like:

I like running bulls. (ambiguous)

So sure, there is some level of ambiguity in example11 because you cannot tell whether the thing you like is the running itself (with bulls its verbal complement) or whether the thing you like is those bulls who just happen to be running.

Thing is, in practice it probably doesn’t matter much though which of these two understandings that ambiguous example 12 works out to being:

I like running the bulls. (gerund phrase)
I like the running bulls. (participial adjective)

In the rare case that it matters at all, inserting something to give away whether you have a noun or a verb as I have done here with the. That’s only needed because running bulls is the object of like. If that were the subject of the sentence then simple subject–verb agreement would tell you which it was, as previously demonstrated in sets A and B:

Running bulls is what I like to do.
Running bulls are what I like to avoid.

What Bill J is talking about is that gerunds can take either adverbs and objects, or take adjectives, but not both.

So both the following are grammatical:

I don't like needless killing.
I don't like killing sheep.

But you can't say:

*I don't like needless killing sheep.

He clearly is classifying the gerund killing as a noun when it has an adjective, and as a verb when it takes an adverb or an object. But if you use this classification, there is no way to tell what part of speech killing is in I don't like killing. And you also have to change the rule that only nouns/noun phrases can be the subjects of sentences (e.g. killing sheep is immoral). This isn't how anybody else classifies gerunds.

You can get around this grammatical restriction by turning the adjective into an adverb:

I don't like killing sheep needlessly,

or by inserting the preposition of:

I don't like the needless killing of sheep.