Please consisder the sentence

Hiking is fun.

What is each word’s part of speech?

  • Hiking = gerund

  • is = verb

  • fun = _____?

I don’t know what fun is here. Is it

  1. an adverb that modifies the copular verb is?
  2. a predicate adjective modifying hiking?
  3. a noun as a predicate complement in the copula?
  • Have a read of the copula article. It should make things more clear. – Matt E. Эллен Nov 6 '13 at 14:15
  • Although the usage of 'fun' as an adjective will doubtless widen. Then we will be able to argue about whether 'fun' in this construction is a noun (as in This is drudgery) or an adjective (This is enjoyable). – Edwin Ashworth Nov 6 '13 at 14:20
  • @ Edwin Ashworth A test I apply is whether it can be qualified by an adjective. (I'm not sure if it is valid or not.) But you can say 'It is good fun', or 'it is appalling drudgery', but to qualify 'enjoyable' would require an adverb like 'remarkably'. So I'm saying 'fun' and 'drudgery' are abstract nouns. – WS2 Nov 6 '13 at 14:31
  • @WS2 That's one test, of course, and it's useful. But not foolproof. A test for adjectives in copulas is that they give an attribute of the subject's referent rather than state an equivalence: “Words are fun” is the grammatical equivalent of saying “Words are boring”. I'm pretty sure 'fun' here is somewhere along the noun - adjective continuum. Neil's test supports this (though he has an {Adj or N?: indeterminate}, ie dual class, rather than gradience, model). – Edwin Ashworth Nov 6 '13 at 14:50
  • Hiking is not a “gerund” here, and “gerund” is not a part of speech. // Here hiking is a noun just as it is in “careful hiking” or in “hiking boots”. If you wanted it to be a verb, then you would need a clause like “Carelessly hiking slot canyons” — at which point the word hiking is at last a verb and the entire clause would be pleased to serve in the grammatical roles of subject or object or even modifier. Substantive roles of ‑ing clauses are what Latinate grammars call gerund uses, and modifier roles participial uses. Parts of speech ≠ grammatical roles. – tchrist Sep 5 at 2:03

In the sentence "Hiking is fun," the word "fun" is an adjective. It's the same type of construction as, for example, "My mother is tall."

The word "fun" can be a noun as well as an adjective, and the verb "is" can link two nouns ("My mother is a teacher"), so I can see where you might be confused. But in the sentence "Hiking is fun," most English speakers would understand "fun" as an adjective, almost as if it were shorthand for "Hiking is a fun thing to do."

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    There are far more Google hits for "is a lot of fun" than for "is really fun" (only 49 million!), indicating perhaps that the nounal perception outweighs the adjectival here. – Edwin Ashworth Nov 6 '13 at 14:34
  • @EdwinAshworth Good information to add, but I do not think it indicates that native speakers perceive "fun" as a noun in the OP's hypothetical sentence. What if you asked a speaker to add some more words to the sentence to further characterize what hiking is? Do you think they would say things like, "Hiking is fun, play, and exercise," or do you think that would say things like "Hiking is fun, easy, and affordable"? – Michael Broder Nov 6 '13 at 14:46
  • Yes, you are free to choose a different argument – nice, too. An Ngram for "is so fun,is such fun" shows that, though the adjectival construction was certainly gaining ground in 2000, it had always been in the shadow of the nounal. Admittedly, raw Google data seems to show that the crossover has occurred – but I'd say these figures are probably skewed by repeats... – Edwin Ashworth Nov 6 '13 at 15:11
  • We'd probably have to do a survey to be clearer about perceptions. Some, especially older, people don't accept 'fun' as an adjective in the first place, though it appears as a marginal one in various dictionaries nowadays. They probably have never even thought about dual membership or gradience, so it has to be a noun. Younger folk commonly use 'fun' adjectivally, so can happily claim this usage as thus. I've got to say that applying various comparator tests really leads to an 'indeterminate' label, but that on semantic grounds, I'm pulled nearer adj than noun by the similar 'words are fun'. – Edwin Ashworth Nov 6 '13 at 15:17

There's little evidence for saying that "fun" is an adverb, but a case can be made for it being either a noun or an adjective. Evidence for it being a noun or adjective would be that it is possible to say either of the following:

Hiking is such fun (and championship).

Hiking is so fun (and exhilarating).

whereas generally when the category of the word is less controversial, such specifies nouns, not adjectives, and so specifies adjectives, not nouns:

*Hiking is such exhilarating/tiring.

*Hiking is so drudgery/championship.

So the answer is essentially that the speaker can make it either a noun or an adjective.


In the given example, 'fun' can be either a mass noun or an adjective, because either can function as the predicative complement of the copula 'is'. Thus, you'd have to dig deeper to figure this out.

The Cambridge Grammar of the English Language (Page 1643) says that the word 'fun' is originally a noun but is recently also used as an adjective, especially among younger speakers:

To establish that a noun has been converted into an adjective we need to show that it has acquired distinctively adjectival properties. Since the ability to modify a noun is not restricted to adjectives this will normally mean showing that it has become gradable and takes the distinctive degree modifiers that are found with adjectives but not nouns, notably very and too. One often-cited example is fun (and the fact that this example is cited so often reflects the paucity of clear examples): many speakers, especially younger ones, accept expressions like a very fun person, indicating that fun has been assimilated into the adjective category.


In formal writing and grammatical education, fun is always a noun. Any use of fun as an adjective is informal and generally not preferred. If you were to come across that sentence in a grammar book "fun" would always be a predicate nominative.

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    This answer is so twentieth century. Dost thou not admit that English changeth? See this Ngram. – Peter Shor Apr 30 at 14:23
  • Fun can be used as an adjective- "I had a fun trip." – Karlomanio Apr 30 at 17:08
