1. An enlightening experiment

Google Books yields only 39 results, and instead asks me if I wanted to say “an enlightening experience”, and eagerly shows an impressive 10,000 results when I click on their suggestion. But for my purposes, I want the noun experiment

  1. A running experiment

Dictionary.com suggests that running in 2. must be an adjective


  1. prevalent, as a condition or state:
    running prices.
  2. going or carried on continuously; sustained:
    a running commentary.
  3. extending or repeated continuously:
    a running pattern.

We normally hear the plural form, running experiments, but the singular form is grammatical, and Google Books produces about 54 results.

Enlightening in "An enlightening experiment" is an adjective because I can use "very" to modify it:

A very enlightening experiment (YES)

but in sentence No.2, running cannot be modified by "very"

A very running experiment (NO)

It makes no sense, even though "running" appears to be an adjective. The comparative form,
“A more running experiment” is evidently wrong, but with enlightening, the comparative is acceptable:
“A more enlightening experiment”.

  • Does that mean running in sentence No.2 is a gerund?
  • How can I prove that running is a participial adjective or a gerund?

This question was inspired by this ELL answer

  • 1
    To be fair, the 'very' modifier placed before the example phrases from your dictionary would make them just as absurd: 'a very running commentary', 'a very running pattern'. I don't think this is the best parameter to test here.
    – Tushar Raj
    Commented Jan 6, 2017 at 11:21
  • 1
    The more I think about it, the more intriguing it gets. Good question. +1.
    – Tushar Raj
    Commented Jan 6, 2017 at 11:26
  • 1
    I think the sense of the word 'running' here restricts some grammatical constructs, or least make them sound absurd. Consider replacing running with ongoing, a close synonym and a more evident adjective. You still can't get rid of the absurdity.
    – Tushar Raj
    Commented Jan 6, 2017 at 11:30
  • 3
    Re It makes no sense, even though "running" appears to be an adjective. You seem to be assuming that if a word can be used adjectivally, it must be gradable. But that doesn't apply to a running tap any more than to, say, a burning bush or an impossible task. Commented Jan 6, 2017 at 15:02
  • 2
    @FumbleFingers I prefer "a slightly runny nose*" not for myself, but in writing you understand :) Only 12 instances on your link by the way. We say "runny cheese" don't we, never "running cheese". Interesting, eh?
    – Mari-Lou A
    Commented Jan 6, 2017 at 16:56

7 Answers 7


In your examples, "enlightening" is best seen as an adjective and "running" as a VP comprising a gerund-participle form of the verb as head.

Taking "running" first: it fails the usual tests for adjectivehood: (a) it can’t be modified by "very" (* The very running man); (b) it can’t occur as complement to complex-intransitive verbs like "become" (* It became quite running); (c) it can’t occur a complement to complex-transitive verbs like "find" (* It found it quite running).

Other examples of VPs as modifiers are an approaching train, a sleeping child, some melting ice-cream.

"Enlightening" on the other hand passes the tests: It can be modified by "very", which can’t modify verbs (A very enlightening experiment); and it can occur as complement to both complex intransitive verbs and complex-transitive verbs: (It became quite enlightening; I found it quite enlightening). Other examples are a very entertaining show; a very fightening film.

That can only mean that "enlightening" when it occurs as an attributive noun modifier is an adjective, while "running" is a gerund-participial verb as head of a VP.

  • 3
    For the benefit of visitors who might be unfamiliar with the acronym, VP stands for verb phrase
    – Mari-Lou A
    Commented Jan 7, 2017 at 9:31
  • Could you please define what a gerund-participial verb is, I only found 14 instances on Google and their definitions do not seem to match my example.
    – Mari-Lou A
    Commented Jan 7, 2017 at 10:26
  • I 100% agree that "sleeping" in "sleeping baby" is a verbal phrase, but I doubt the same word in "sleeping town" is a verbal phrase. It is closer to ungradable adjective. That's what I raised in my answer. Again, the test is useful, but not perfect.
    – user140086
    Commented Jan 7, 2017 at 15:37
  • @Rathony When we say "sleeping town", we are of course referring to the townfolk, not the buildings. It's no different to "sleeping child", so the test is fine.
    – BillJ
    Commented Jan 7, 2017 at 19:12
  • 1
    The similarity is of course that verbs like "sleeping" have the same function as genuine adjectives, that of modifier (a sleeping child / a naughty child). And the same applies to "sleeping" (a sleeping / peaceful town. You have to perform the tests I mentioned in order to decide word category. "Sleeping-bag" is different; it's a noun-centred compound noun (gerund-participle verb + noun).
    – BillJ
    Commented Jan 7, 2017 at 20:33


  • Despite running being in origin the -ING inflection of the verb to run, in your “a running experiment” example, it is no longer a verb and therefore ᴄᴀɴɴᴏᴛ be either a gerund or a participle either. A rule of thumb is that “No verb = No gerund–participle”.
  • Here it’s almost certainly an adjective because it passes the Predicate Test, but it may under certain exotic readings be a noun instead.
  • The OED calls these former -ING verbs participial adjectives and deverbal nouns respectively.

Your Question

You’ve asked whether in

  • a running experiment

The word running is a “gerund” or a “participle” — or an adjective, and you propose a gradability test to see whether something is an adjective. This bothered you because as an adjective, running isn’t all that gradable.

Gradability is one test for adjectives, but not the only one. Another and perhaps stronger adjective test is the predicate test. This test distinguishes adjectival uses from nouns used attributively.

The Predicate Test for Adjectives

The way this one works is that given a noun phrase containing a pair of words “Y X”, where X is a noun but you aren’t sure whether the Y in front of it is an adjective, you look at the copula created by placing Y in the predicate positions and saying that “X is Y”. Then you decide whether that copula means the same thing as the original Y–X pair means. If so, then Y is (probably) an adjective. If not, then something else is going on here.

First, let’s show that the test works for other cases. When one says that “someone is in the dog house”, you know that with dog house you have a noun phrase here because it has a determiner (the definite article) and it is itself the object of the preposition in. But you don’t know whether in dog house, that first word dog is a noun or an adjective. The copula you need for the predicate test is therefore “house is dog”.

Does it still mean the same thing? Can you switch “dog house” to “house is dog”? Try it:

  • someone is in the dog house
  • someone is in the house (that) is (a) dog

No, you cannot, because in fact the house is not a dog at all! Rather, the house is for dogs! Dog is not an adjective. Rather, dog is a noun in attributive use. Further evidence that dog is a noun here is that you can restore the original sense by inserting a preposition (ᴘʀᴇᴘ) like for, by, with, from in your “Y is ᴘʀᴇᴘ X” copula. That means you know you have two nouns.

A running experiment

So, let’s try it. Create a “X is Y” copula:

  1. running experiment
  2. experiment is running

Does that mean the same thing? Does it make sense? If so, then running is an adjective.

I rather expect this to be the case you mean here. There is, however, another possible read, one which needs ᴘʀᴇᴘ to make it read correctly in the copula:

  1. experiment is about running

Are you doing experiments on running? If that’s the sense you mean it in, then no, running is not an adjective there, but rather a noun.

Wait, I asked about participles versus gerunds!

So you did, so you did. Fine, but first let’s establish some ground rules to make sure we agree on what we’re talking about:

  1. A gerund is a verb in its -ING inflection that heads a verb phrase used somewhere the grammar requires a noun phrase.
  2. A participle is a verb in its -ING inflection that heads a verb phrase used somewhere the grammar requires a modifier phrase.

Yes, that’s a mouthful, which is why I wanted to make sure we understood the difference between nouns and adjectives first before addressing the question asked using the terms it asked about.

It’s such a mouthful that people often cut corners and pretend that gerunds and participles are nouns and adjectives. But they are not. Gerunds and participles are both verbs. They are neither nouns nor adjectives. The only difference is that the verb phrases they head are used in place of a noun phrase in the “gerund” case versus being used in place of a modifier phrase.

So a gerund phrase is an -ING verb phrase used substantively while a participle phrase is an -ING verb phrase used um “modificationally”. (SORRY!)

There isn’t a lot of difference there, and sometimes the example is simply too short to say one thing or the other. But what’s key is that you can use the predicate test here to winnow out the noun-like gerund-phrase case from the adjective-like participle-phrase case.

However, you’re going to have to apply some verb tests first to make sure that these are really verb phrases. If you can’t get any of the verb tests to pass but you can get noun or adjective tests to pass, then you do not have a verb. You just have a noun or an adjective.

The Object Complement Test for Verbs

One of the best verb tests we have the object complement test. Does the would-be verb take a direct object and perhaps an indirect object? Of course this only works for verbs that can ever take objects at all, meaning transitive verbs, but so be it.

Running can take an object, because you can run errands or races or drugs. It can even take an indirect object if you’re running someone an errand. Is this an experiment about running things?

If this were an experiment about running drugs, then sure. If you put your drugs object in front of the verb as is customary, then you have a drug-running experiment.

Notice though that I’ve needed that pesky preposition about there. The predicate test fails without it! So this verb phrase is not being “used as an adjective”. Rather, this verb phrase is being used substantively, being used in place of a noun phrase.

That leads us down the gerund fork not the participle fork.

An aside for noun tests

Understand that drug running is a compound noun, because running is a noun not a verb. You can tell by using noun tests on it. A noun has a particular slot in a noun phrase, so if you can use running there, then it is a noun. Determiners like his and adjectives like constant come before nouns, so try it:

  • His constant drug running doomed him to an early death.

That proves that running is a noun. So does this:

  • His constant running of drugs doomed him to an early death.

In fact, that’s still a noun without the drugs involved.

  • His constant running doomed him to an early death.

So those runnings are nouns. That isn’t what we have here though. Probably.

Fine, fine: but which is it, gerund or participle?

I actually don’t think it’s either, because it’s not a verb here. There aren’t any objects, and really, you can’t put any there either, not in the normal way.

So I don’t believe that running is a verb in your example of a running experiment. According to the ground rules we established at the top of this section, it has to be a verb to be either of those two things. And since it is not a verb, it must be neither.

Here running passes the object-complement test for verbs (drugs being the object*, so here it is indeed a verb:

  • He has been running drugs all his short life.

This is also a verb example, but different:

  • What scared her the most was him constantly running drugs instead of making an honest living.

Both those are examples with running as verbs with verbal complements, which means that as verbs they’re so-called gerund–participles not nouns or adjectives, with no finer distinction necessary. It’s that they’re verbs that matters.

But you don’t have a verb in your example, only a former verb that’s now either a noun or an adjective.

So are my running experiments using running as an adjective or a noun?

If you can get it to pass the predicate test without having to add a preposition to connect two nouns, then you’re probably talking about an adjective here.

Which of these two works?

  • the experiment is running
  • the experiment is about running

It’s your experiment so you’ll have to tell me, but I’m going to guess that the first applies and the second fails.

That means that running is here an adjective.

Which, you’ll note, is what your dictionary entry duly reported in the first place.

Mind you, many dictionaries get this sort of thing wrong or gloss over it too much for a correct reading. But this one, I think, has the right of it.

What the OED says about these

The OED categorizes -ING words that are no longer verbs as nouns and adjectives, but it qualifies that in some cases calling them verbal nouns and participial adjectives. (BTW, you’ll find other sources referring to ex-gerunds as de-verbal nouns instead of as verbal ones. Same diff.)

And in point of fact, running may be either of those according to the OED. It has one entry for running labelled “ppl. adj.” but another entry for running labelled “vbl. n.”

There are lots of ex-verbs that can have both flavors:

  • acting: an acting mayor (ppl. adj.) versus an acting school (vbl. n.)
  • living: a living creature (ppl. adj.) versus a living space (vbl. n.)
  • singing: a singing bird (ppl. adj.) versus a singing lesson (vbl. n.)

Again, these are all ex-verbs, so they cannot be gerunds or participles. What’s left behind once you’ve defrocked them of their verbal entourage is just an adjective or a noun, not a verb.

Ear training exercises

Here’s something that may help here, at least if you’re a native speaker. In speech, native speakers easily create and recognize the distinction of using an -ING (participial) adjective versus using using an -ING (verbal) noun there using stress. Except under emphasis, the adjective -ING word in front of the noun doesn’t take primary stress in the phrase, but the noun one does: a singing BIRD versus either of a SINGING lesson or a SINGING LESSON.

  • 1
    I will give you another comment, if necessary, as I haven't read it completely. Just because you can construct "a running man" and "a man is running" doesn't mean running here is an adjective. It is closer to a verb in the form of present participle. If you contrast it with "burning sensation" and "sensation is burning", you can't tell whether burning is an adjective or a present participle. I would say it is closer to an adjective. I have seen many explanations where people try to determine a part of speech using a test, but I don't think there is a perfect test.
    – user140086
    Commented Jan 6, 2017 at 16:03
  • 4
    Why couldn't "running" in "The experiment is running" be a present participle? This would just be the progressive construction, wouldn't it?
    – herisson
    Commented Jan 6, 2017 at 16:27
  • 1
    It can be argued that running is or can be a participle in "the man running" (whether through ellipsis or another agency), but I agree that it must be an adjective, not a verb, in "the running man."
    – Robusto
    Commented Jan 6, 2017 at 16:43
  • 1
    @Robusto Good point. If the word "running" in "the running man" means "on the run to avoid being captured by authorities", it should be an adjective. Again, it is used metaphorically. It doesn't necessarily mean "running" in "a running man" is an adjective.
    – user140086
    Commented Jan 6, 2017 at 16:51
  • 1
    @Rathony In a running man it is an adjective albeit one of the participial variety, meaning it was once a verb but no longer is so because it no longer does verb things. In A man is running it is a verb because it can still do verb things like A man is running down the street and A man is running errands for his wife. You cannot add down the street or errands for his wife to the participial adjective because it is no longer a verb the way it is when used in progressives. A participial verb is a verb not an adjective, a participial adjective is an adjective not a verb.
    – tchrist
    Commented Jan 6, 2017 at 17:01
  1. I saw a running man. 2. There was a running experiment. 3. He had an extremely running (runny) nose.

In No. 1, the word running is definitely a present participle (verb). However, it is difficult to say it is a present participle in No. 2 and No. 3 as the verb run is used metaphorically and it can be changed to "on-going, continuous, etc." in No. 2 and "mucus-discharging" in No. 3. In other words, an experiment and a nose can't physically run and both of them are used metaphorically. The distinction doesn't seem to be very clear and whether it is a present participle or an adjective will depend on how you interpret the verb run in each example.

It's somewhat wrong to assume that all adjectives in English can take "very" as an adverb to emphasize their meaning and "more" to construct a comparative sentence. Some adjectives, especially those derived from -ing forms or past participle forms, don't take either. For example,

He is married.

The adjective married means "united in marriage". But the following sentences sound unidiomatic unless they are used metaphorically:

*He is very married. *He is more married than she (is).

The reason is the adjective married itself describes a state that can't be emphasized further or compared. In order for such an adjective to take either "very" or "more", it should get some help from another adjective or adverb, e.g., happily as in:

He is very happily married. He is more happily married than she (is).

The adjective running belongs to the same category of adjectives that can't take either "very" or "more". If you want to use one, it should take another word such as "long" or "short" as in

Very long (short)-running experiment. Longer (shorter)-running experiment than X.

Some grammar books call them "ungradable or non-gradable adjectives":

Some adjectives describe qualities that are completely present or completely absent. They do not occur in comparative and superlative forms, and cannot be used with adverbs such as very or extremely, because we don’t usually imagine degrees of more or less of the quality being described. They are referred to as non-gradable adjectives. Non-gradable adjectives do sometimes occur with non-grading adverbs such as completely which emphasize the extent of the quality.

(emphasis mine)

Some ungradable adjectives described in this link can take "very" and "more". There seems to be no hard-and-fast rule and it will entirely depend on whether an adjective sounds idiomatic or not with "very" and "more".

  • 1
    It's a good answer so it's +1 but I have heard of men who were described as being "very married", meaning that they were either devoted husbands, or they would never leave their wives.
    – Mari-Lou A
    Commented Jan 6, 2017 at 12:07
  • 2
    @Mari-LouA My conclusion is at the end it will entirely depend on whether an adjective sounds idiomatic or not with "very" and "more".
    – user140086
    Commented Jan 6, 2017 at 12:35
  • 1
    @Mari-LouA Also, you should note that "very married" or "extremely married" could be understood as the meaning of the adjective expanded over the years and "He is very married (committed in a sense) to his work/profession" sounds more idiomatic than just "He is very married (united in marriage)." and they should be understood metaphorically rather than literally.
    – user140086
    Commented Jan 6, 2017 at 12:56
  • 2
    @tchrist "Running" can't be an adjective on several counts: It can't be modified by "very" (* A very running man); it can't occur as complement to complex-intransitive verbs like "become" (* It became quite running); it can't occur as complement to complex-transitive verbs like "find" (* I found it quite running). As an attributive modifier in an NP like A running man, "running" can only be a gerund-participle verb heading a verb phrase. The same applies to items like a sleeping child, these melting marshmallows, a gleaming showroom and the like.
    – BillJ
    Commented Jan 6, 2017 at 16:19
  • 3
    @tchrist Yes, but they define it as "The action or practice of smuggling illegal drugs", which would of course be a noun, cf. Drug-running is a major source of concern for everyone. But when it modifies a noun, it can only be an adjective (compound verb-centred). It's a very productive type of compound adjective; some examples are gradable such as an incredibly breath-taking view and a very heart-breaking story, while others are normally ungradable and restricted to attributive function: a cost-cutting exercise, a fact-finding mission.
    – BillJ
    Commented Jan 6, 2017 at 19:17

There is much good discussion in the other answers. This is an historical note.

In Aspects of the Theory of Syntax (1964), Chomsky considered the phrase "the sleeping child", and argued that it is transformationally derived from ?"the child sleeping" by Modifier-Preposing, and in turn that comes from the relative clause construction "the child who is sleeping" by Relative-Clause-Reduction (or WHIZ). I am giving here a rather free paraphrase of Chomsky's argument.

He gave as evidence for his analysis, the ungrammaticality of *"the child who very sleeps" and *"the child who is very sleeping", which is obviously due to the fact that "very" can't modify verbs. From this constraint, and from the transformational derivation above, it follows that *"the very sleeping child" should be ungrammatical. Thus transformational grammar (TG) explains why "very" cannot modify the modifier "sleeping". In traditional grammar, this fact appears mysterious and would require an ad hoc constraint.

Is this a fair argument by Chomsky? Yes, but only in (what we would now call) classical TG. In the theory described by Chomsky, subcategorization constraints based on lexical categories (the parts of speech) have meaning only for deep structures, before any transformations apply. It is not necessary to appeal to a category of "participle-modifiers" to explain special properties of the "sleeping" modifier, and in fact it isn't even possible. Lexical constraints like the one under discussion are relevant only to deep structure, and in deep structure, there is no modifier "sleeping" -- only the progressive aspect of the verb "sleep", which occurs within a relative clause.

I think this is an important difference to know about between traditional grammar and TG. Above, I use the phrase "classical TG" sometimes, because not all contemporary forms of TG are like the original version of TG as described by Chomsky in Aspects. McCawley's version of TG, for instance, is deliberately different in this respect from the classical TG of 1964. As for CGEL, it seems to be a hodge-podge; I doubt the authors know what syntactic theory they are using.

  • I believe you are suggesting that running experiment is an example of WHIZ, aren't you? And you disagree that running is a gerund-participial verb. I don't have access to CGEL (too damn expensive a book for me to buy) but I did find this Language Log post that mentions this linguistic term.
    – Mari-Lou A
    Commented Jan 7, 2017 at 10:04
  • +1 for Relative-Clause-Reduction because "This is an experiment that is running" makes sense. But running is still an adjective, it is an example of a reduced adjective clause. Please correct me, if I'm mistaken.
    – Mari-Lou A
    Commented Jan 7, 2017 at 10:32
  • 1
    @Mari-LouA, I wasn't really advocating for or against a term; I was repeating the explanation proposed by Chomsky in Aspects (because I thought it was being lost sight of). I don't see any point in arguing about terminology. Use terms according to your own convenience.
    – Greg Lee
    Commented Jan 7, 2017 at 17:36
  • In "a sleeping child", "sleeping" is undoubtedly a verb functioning as modifier. It can't be an adjective since (1) it can't be modified by "very"; (2) it can't be complement to complex-intransitive verbs like "become" (* "It became quite sleeping"); (3) It can't occur as complement to complex-transitive verbs like "find" (* "I found it quite sleeping"). The range of expressions that can occur as pre-head modifier to a noun is very large and varied: we don't want to call them all adjectives. It's a VP.
    – BillJ
    Commented Mar 6, 2022 at 13:15
  • Based on your free paraphrase of Aspects of the Theory of Syntax, Chomsky seems to consider sleeping to be a verb, doesn't he? If so, that's exactly what H&P's CGEL is saying, so I don't understand why you'd call it "a hodge-podge". Please enlighten me.
    – JK2
    Commented Feb 4, 2023 at 14:46

Short answer

I think “running” in “a running experiment” is the same part of speech as “running” in “an experiment that is running” (so to that extent, I agree with Greg Lee’s answer).

What to call this part of speech depends a bit on theory, but I think a fairly safe noncommittal term is “participle”. This is the “present” or “progressive” participle, of course, not the “past” or “passive” participle.

In mainstream analyses of English that I am familiar with (like CGEL 2002) , participles are classified as verb forms, so the part of speech would be “verb”.

However, there are also arguments for classifying participles as a type of “adjective”.

I would only call it a “gerund” if I was using an analysis that doesn’t distinguish between present participles and gerunds, and I think the usual terminology used in analyses like this is “gerund-participle”. (As far as I know, this unified analysis only occurs in theories which say the “gerund-participle”’s part of speech is “verb”.)

Long answer

This is a very difficult and deep question. As far as I can tell, not even linguists agree about what part of speech “running” is in a phrase like this, or how it functions grammatically. You have already brought up most of the relevant established facts; any explanation beyond that is likely to be debatable and dependent on specific linguistic theories. I know very little about these, but I did read a couple of papers that I found interesting and that might be of interest to you as well.


Terminology is difficult, especially when dealing with different theoretical backgrounds. However, I think it might help to go over some terms and how they are commonly used to avoid confusion later on.

Participle. For people who use this term, it refers to certain word forms that in English are morphologically composed of a verb base and a participle-forming suffix. English has two types of participles.

  • The “past participle” is usually formed with the suffix -ed, or more rarely -en, -t, a zero suffix, or a vowel change. It appears in the passive construction after a form of to be (e.g. The pie was eaten by your cousin), and in the perfect construction after a form of to have (e.g. Your cousin has eaten the pie). Of course, not all word forms that look like participles are participles. The word form “kicked” looks like a past participle, but in a sentence like Pat kicked Sandy, “kicked” is not a past participle, it’s a past-tense verb. (But “kicked” is a past participle in Sandy was kicked by Pat.)

  • The “present participle” is always formed with the suffix -ing. It appears in the progressive construction after a form of to be (e.g. Your cousin is eating the pie). I think most linguists would say that not all words that look like present participles are present participles, but it’s hard for me to find a good theory-neutral example of a word that looks like a present participle but definitely isn’t. I guess the noun “gelding” works, as in The horse was a gelding: this looks like a present participle, but it definitely isn’t one. (In contrast, “gelding” would definitely be a present participle in a sentence like The farmer is gelding the horse.)

Gerund. For people who use this term, it refers to a certain word form that in English is morphologically composed of a verb base and a suffix -ing. It seems to be used to refer to slightly different sets of things by different people, but the common point is that gerunds are, or at least can be, “nouny”. I don’t think “running” in “a running experiment” bears much if any resemblance to a noun, so fortunately I think I can avoid discussing gerunds in the rest of this post.

Gerund-participle. It is a currently unsettled issue whether the “present participle” in English should be considered a distinct word form from the “gerund”. In standard English, there is in principle no way of distinguishing the two by either sound or spelling. That is why they are sometimes referred to as a single form called the “gerund-participle”; Pullum and Huddleston’s Cambridge Grammar of the English Language argues for this analysis.

Adjective. The meaning of “adjective” is fairly clear in one respect: it’s easy to give examples of words that anyone would agree are adjectives, such as happy, sad, important, colorless, historical, perfect, dead. It’s much more difficult to define exactly what makes these words adjectives; this is where you get competition between different theories. Linguists generally agree that, if a word behaves similarly in grammar to other words that are known to be adjectives, that constitutes evidence for it being an adjective as well.

Verb. In the analyses of English grammar that I have any familiarity with, verbs are defined as a class of words. In English, these words take different forms; for example, the verb steal takes the suffix -s in its third-person singular present-tense form “steals”. This is called “inflection”, and it isn’t considered to change steal into another word or another part of speech: it’s still the same word, and it’s still a verb. “Steals” is what is called a “finite” form of the verb: it can be used in an independent clause like The robber steals the treasure. The grammars I am familiar with also recognize “non-finite” inflected forms of verbs, namely, the infinitive (which is just “steal”; it doesn’t have a special suffix), the past participle “stolen”, and the present participle and gerund/gerund-participle “stealing”. These non-finite forms are also considered to be the same word as the finite forms of steal and the same part of speech; i.e. in Your cousin is eating the pie, “eating” is considered to be a verb: it is the word eat inflected into a certain form. Apparently, there are other approaches to dealing with the part-of-speech classification of non-finite forms, but I am not familiar with them. It seems in Distributive Morphology, a non-Lexicalist theory of grammar, “the same Vocabulary item may appear in different morphological categories depending on the syntactic context that the item’s l-morpheme (or Root) appears in”, so there are no such things as nouns, verbs and adjectives in the traditional sense. (“Distributed Morphology: Frequently Asked Questions List”, maintained by Rolf Noyer. Note that this is not a mainstream linguistic theory. Also, here is a related question on Linguistics SE: Are there any languages with minimal distinctions between the noun and verb categories?)

Participial adjective. As far as I can tell, people just use this as a term meaning “an adjective derived from a participle”. In other words, “participial adjective” is a label for a word that IS considered to be an adjective, and is NOT considered to be a participle. Hopefully I’ve understood this correctly. I can imagine some people might use it with the sense “an adjective that is simultaneously a participle”, but that isn’t what I would expect it to mean without further clarification.

Relevant points re-summarized

You already pointed these things out in your question, but I think it will help me organize my answer to repeat them. Also, these are the least controversial parts of this post.

At least some words that end in -ing are adjectives, like enlightening

As far as I know, everyone agrees that at least some words that end in -ing are adjectives.

Also, I think everyone would agree about some specific cases of this; for example, that the word enlightening is an adjective in a phrase like “a very enlightening experiment”.

“an enlightening experiment” is different in some ways from “a running experiment”

You’ve already noticed that we can use a comparative construction with more or most before enlightening (“a more enlightening experiment”), but not before running (*“a more running experiment”). BillJ explains the significance of this better than I do, and Rathony explained it before me. The observation is simply that enlightening is gradable. This is more or less the same thing we test for with the very test (“a very enlightening experiment” vs. *“a very running experiment”).

As Rathony says, the gradability test with very is unfortunately inconclusive here. Only adjective phrases are gradable in this way (I think everyone agrees on this point), but not all adjective phrases are (easily) gradable. So the gradability test can be used to prove that something is an adjective, but it can’t be used to prove that something is not an adjective: a negative result doesn’t tell us anything for sure. Running in “running experiments” does not seem to be gradable, but it still might be an adjective or a verb.

There are also some differences in how we can use enlightening and running after verbs. BillJ points out two parts to this:

[enlightening] can occur as complement to both complex intransitive verbs and complex-transitive verbs: (It became quite enlightening; I found it quite enlightening). Other examples are a very entertaining show; a very frightening film.

I think another complex intransitive verb phrase like “become” may be “stop being”, as in “The experiment stopped being enlightening” vs. *“The experiment stopped being running” (Google Ngrams doesn’t return any results for “stop being running”).

Apparently, verb tests like these show that enlightening is an adjective. But unfortunately, as with the gradability test(s), it’s less clear if failing the verb tests means that running is not an adjective.

Apparently, there is such a thing as adjectives that can’t be used predicatively, including some participial adjectives such as alleged. It doesn’t quite work to say that running is always a non-predicative adjective, since it can be used in sentences like “The experiments are still running”, but it seems like it could be an adjective of another type, neither always able to be used predicatively or never able to be used predicatively, but only able to be used predicatively in certain circumstances.

In fact, I found a fairly recent paper that says that non-gradable adjectives generally cannot be used as the complement of “seem”. “The Category of Participles”, by Björn Lundquist (2013), cites an argument to this effect by O. Matushansky in “Tipping the scales: the syntax of scalarity in the complement of seem” (2002). Lundquist gives the following example

(12) a. This music seems nice/*choral.
b. This problem seems insoluble/*mathematical.
(from Matushansky 2002)

It’s a bit difficult to make this clear however because of something called “scalarity coercion”: basically, most adjectives can be gradable, given the right circumstances, even if they are normally non-gradable. The example of this that Lundquist gives is

(13) a. This music seems almost choral.
b. This problem seems pretty much mathematical.
(from Matushansky 2002)

(Lundquist’s main argument is that all participles are actually adjectives, but I’ll get into that later.) Anyway, if Matushansky’s argument is correct (I’m not sure that it is, because the issue of “scalarity coercion” makes it difficult for me to judge the grammaticality of these examples), it seems like the same explanation might apply for complements of verb phrases like “become”, “find”, “stop being”. That would mean that the verb tests don’t give us much, if any more information relative to the very test or the comparative test: it might just all be about gradability.


So far, I’ve just been summarizing the data and facts that I am aware of that seem relevant (in a probably long-winded manner). How to interpret these facts seems to be controversial. I’ve read two papers so far and encountered at least three different approaches.

Bresnan, as presented in Laczkó: “running” has to be an adjective when it comes before a noun, but it could be a verb in some other context

The first paper I read was “Another look at participles and adjectives in the English DP”, by Tibor Laczkó (2001). He cites Joan Bresnan (unpublished) as saying that smiling in phrases like “a smiling child” is an adjective.

This follows from a diagnostic principle that Laczkó presents as follows:

Adjectives but not verbs (including participles) can be prenominal modifiers: A N vs. *V N.

This diagnostic isn’t obvious to me personally, but it seems to have some appeal to many people. Laczkó in fact says in a footnote that

It is important to note that this view is quite dominant in the literature, whether generative or non-generative. For instance, Levin and Rappaport (1986) appear to share Bresnan’s empirical generalizations, but in their GB framework they offer an analysis different from Bresnan’s LFG approach. (Here I cannot discuss and compare these two accounts.) In addition, Ackerman and Goldberg (1996) also consistently talk about English “deverbal adjectives based on past participles and used attributively”. (footnote 7)

As far as I can tell, tchrist’s answer classifies running as an adjective due to something like this principle.

Incidentally, Laczkó also mentions another useful diagnostic test from Bresnan: only adjectives can be preceded by the negating prefix un- (but don’t confuse this with the rarer and less productive reversative prefix un-, which attaches to verbs such as undo, unlock). But I don’t think we can say that all adjectives can be preceded by un-, so it doesn’t seem like a negative result is conclusive. Checking unenlightening and *unrunning on Ngrams shows that this is another test for adjective-hood that gives a positive result for enlightening, and an inconclusive result for running. (I don’t know if this tests for the same thing as the gradability tests; I’m inclined to think that it does not, since we can very easily say things like unmarried.)

Under an analysis like Bresnan’s (as represented in Laczkó), a term like “participial adjective” would be appropriate.

Laczkó: verbs can occur pre-nominally or post-nominally, just like adjectives. “Running” could be a verb here

Laczkó’s own view seems to be presented in the following passage:

I would like to make the following assumptions and generalizations.

A) Prenominal modifiers are not necessarily adjectives: they can also be participles; and certain postmodifying participle-looking words must be taken to be participles in any analysis.

B) Thus, it is not possible to capture the use of all prenominal participle-looking words in NPs by the help of a single general rule [...] We need two (sets of) rules: one for the use of -ing and -en participles and another for participle → adjective conversion.

C) The relevant generalizations for -ing forms are as follows.

Ca) Participles derived from any one of the three major verb types (unaccusative, unergative and transitive) can be used in NPs, cf.:

a. I couldn’t catch the tile falling from the roof.
b. I couldn’t catch the falling tile.
c. The boy shouting at that girl used to be my friend.
d. The shouting boy used to be my friend.
e. The boy reading a newspaper used to be my friend.

(3.2. Participle-looking words in English NPs revisited)


In this paper I have challenged the quite general view that the overwhelming majority of participle-looking words in English NPs (including all the prenominal ones) are adjectives and claimed that they are participles (non-finite verb forms). (4. Concluding remarks)

His arguments include the very test, the acceptability of phrases like “a crying child” alongside the unacceptability of sentences like “*The child was too crying last night,” and the fact that English attributive adjectives can occur post-nominally as well as pre-nominally (suggesting that there is no absolute link between adjectival status and pre-nominal position). I didn’t find any absolutely compelling argument that e.g. would convince someone devoted to another theory, but Laczkó’s viewpoint makes more sense to me than Bresnan’s (at least, as he presented them; I haven’t read any of Bresnan’s actual writing). As far as I can tell, it also corresponds better to the positions outlined in BillJ’s answer, and Greg Lee’s answer based on Chomsky, which makes me a bit confused about Laczkó’s statement that the “dominant” view in all linguistic literature is that pre-nominal -ing words cannot be verbs.

Anyway, from Laczkó’s perspective, I believe “running” in “a running experiment” would be classified as a participle and as a verb.

Lundquist: all participles are always adjectives and never verbs

I alluded to this earlier, but it’s a bit difficult for me to explain Lundquist’s position because unlike Laczkó’s, it does not mesh with my first thoughts about this topic. But, I found Lundquist’s paper thought-provoking. As I mentioned earlier, it seems to be much easier to prove that an -ing word is an adjective than to prove that it isn’t. Lundquist’s view is that all participles are actually adjectives; it’s just that some are gradable and some are not. The way he explains this is by saying that some participles contain an “event structure” (these generally correspond to what others identify as verbal participles) and others do not (these generally correspond to what have traditionally been identified as adjectival participles or participial adjectives). Somehow, the presence of an event structure is incompatible with gradability. It’s a bit much to wrap my head around (Lundquist apparently works in a “non-lexicalist framework”) but there are some useful factual observations that are actually relevant no matter what theoretical position you take. Lundquist notes that

the restriction on attributive participles is much less strict than the distribution of participles following e.g. seem, as shown in (7):

(7) a. the recently made headway—all that headway was/??seems made in a day.
b. the most recently taken photos—these photos were/??seem taken recently.
c. the kicked out guests—they were/??seem/??seemed kicked out.

As shown in (7a), even idiom chunks can appear in prenominal participle phrases, which we can take as evidence that the participle has a phrasal source, and can thus not have been derived in the lexicon (see Kratzer 2000 for discussion). It is not obvious that there is any restriction at all on so-called “verbal” participles to be used as prenominal attributes. [...] there is no reason to assume that only “adjectival” participles, i.e. participles that are event/argument structurally reduced, can be used as pre-nominal attributes, at least not in languages like English and German (though it could of course be the case that some languages only allow adjectives with certain scalar properties in pre-nominal position). (pp. 3-4)

From Lundquist’s perspective, it seems “running” would be classified as a participle and as an adjective (but it seems it would be an “event structure adjective” in particular, and Lundquist writes that “there are no lexical event-structure adjectives” (p. 11) so he would probably say it is not derived in the lexicon).

References (also linked to in-text)

Laczkó cites unpublished (at the time) work by Joan Bresnan, and Lundquist cites “Tipping the scales: the syntax of scalarity in the complement of seem” (2002), by O. Matushansky.

Further reading I haven’t gone through yet

These sources were not used in the writing of this answer; I am linking to them because I encountered them later on and they seem relevant.

  • Adjectival present participles: an aspectual constraint”, by Aya Meltzer (I’ve looked at it a bit and would highly recommend reading it; it describes many, maybe all of the tests I mention here, and also a number I didn’t know about)

  • Participles, gerunds and syntactic categories”, by John Lowe (2016)

  • Remarks on gerunds”, by James P. Blevins (2003)

  • “Word formation is syntactic: adjectival passives in English”, by Benjamin Bruening (2014). This discusses issues of syntax vs. lexicon, and also has an appendix that talks about the word-class categorization of participles (in this case, passive participles, but I think a number of the arguments would be applicable to active participles also)

  • So to be clear, you're saying that "running" is being used like a verb, or it is a verb?
    – Mari-Lou A
    Commented Jan 6, 2017 at 16:17
  • @Mari-LouA: I would say it is a verb, in its -ing participle form.
    – herisson
    Commented Jan 6, 2017 at 16:19
  • If running is a verb in “a running man”, then it must be able to do verb things, and I can't think of any that it can. In the progressive verb “A man is running” it is a verb because it can still do verb things like A man is running down the street and A man is running errands for his wife. You cannot add down the street or errands for his wife to running in a running man. If you could, then it would be a verb not an adjective. In contrast, in “a man running errands for his wife”, now running is a verb again not an adjective. Summary: pre-posed=adjective, pos-posed=verb.
    – tchrist
    Commented Jan 6, 2017 at 17:06
  • 1
    @tchrist: Normally you can't add things to pre-posed adjectives either. For example "a happy man" turns into "a man happy to be free". I don't see how part of speech is relevant to the issue of position before or after the noun; adjectives and participles seem to me to behave more-or-less identically in this regard. What I (and apparently Laczkó) cannot figure out is why the mere fact of pre-position is considered enough to determine that a modifier is an adjective. "Dog" in "dog house" is pre-posed, but we don't call that an adjective.
    – herisson
    Commented Jan 6, 2017 at 17:09
  • 2
    @tchrist: Well, there are apparently some pre-posed modifier tests we can use to distinguish adjectives and participles ("very" for adjectives, and apparently "carefully" for participles) but the problem is none of the distinctive pre-modifiers seem to be possible in "running experiments".
    – herisson
    Commented Jan 6, 2017 at 17:20

When we use running as a noun — for example, “Running is her hobby” — it is said to be a gerund.

And when running is used as adjective — for example, “The hotel did not have running water” — it is said to be a participle.

  • I have kindly reformatted your post to use mixed case instead of ʟᴏᴏᴋɪɴɢ ʟɪᴋᴇ ᴀ ᴛᴇʟᴇɢʀᴀᴍ ʙʏ ʏᴇʟʟɪɴɢ ᴀᴛ ʏᴏᴜ. 😉 That said, what you say is true under some older analyses but untrue under many modern ones. Under these, once an -ing inflection stops doing any “verb” things like having objects and starts doing noun or adjective things only, those analyses now refer to it as just a noun (or even a deverbal noun) or just an adjective (or even a deverbal adjective or a participial adjective). Gerund-participles are always still verbs; they haven’t been “de-verbed” yet.
    – tchrist
    Commented Feb 26, 2018 at 14:36

I'm not a native speaker myself, but I think it is very simple to understand and distinguish what is a gerund, or a gerund functioning as an adjective or a participial phrase.

First, we should understand that a gerund is a verb functioning as noun. For instance, "Swimming is as good exercise as walking." Swimming is a noun, so it is a gerund. Another example: " My father's favorite pastime is playing golf." Playing, here, is not a verb. It is a noun.

When it is an adjective, the gerund form comes before the noun it qualifies: "You're a crying baby, little brother!"; "The speeding car crashed into a lamppost, killing the two occupants instantly." Of course, as far as grammar is concerned, there's a lot more to learn on how to use it, and reading will go a long way in helping one.

  • 2
    To me, it doesn't seem simple, but this may be in part a matter of terminology. Could you explain more how you define the word "gerund"? You say it is "a verb functioning as a noun", but then later in your answer you say "When it is an adjective, the gerund form..." How can the gerund, which is a verb functioning as a noun, ever be an adjective? Did you mean to use the word "participle" in this section instead of "gerund"?
    – herisson
    Commented Jan 10, 2017 at 22:34
  • Check this definition for what participles are all about. You should keep in mind that words have functions, and as such their definitions will depend on what position they happen to be in the sentence. "Participles are words formed from verbs that can function as adjectives or gerunds or can be used to form the continuous tenses and the perfect tenses of verbs. There are two participle forms: the present participle and the past participle." Hope this will help appease your wondering( and maybe wandering) mind.
    – user212771
    Commented Jan 11, 2017 at 1:09
  • Thank you for submitting an answer but you didn't answer the question which is: How can I prove that running is a participial adjective or a gerund? Your post suggests that the position of a word is enough to identify its role, which I had already done, it is what comes later that interested me. Once a word's function has been identified, grammarians/linguists then propose experiments to test that theory. If you read the other answers (because I don't think you have) you'll see that they propose solutions and methods to prove that running is a participial adjective or not.
    – Mari-Lou A
    Commented Jan 11, 2017 at 6:26

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