When I read a sentence, I can identify nouns. But now I need to give proof that they are indeed nouns, and that is where it goes wrong. I can think of one or two things sometimes (like combining it with an adjective), but that is not enough proof.
So my question is, how can I prove in multiple ways that the word is actually a noun?
There is no single syntactic or distributional property of nouns which is sufficient to guarantee the inclusion of an item in the word class.
For most modern grammarians there is a major subcategory of the noun class, the ᴘʀᴏɴᴏᴜɴ, the members of which show slightly different properties and distributions. The remainder of the class can be subdivided into the subcategories of ᴄᴏᴍᴍᴏɴ ɴᴏᴜɴ and ᴘʀᴏᴘᴇʀ ɴᴏᴜɴ. Again, proper nouns have certain properties which mark them out from common nouns. For the purposes of this answer, I am concentrating solely on common nouns. Common nouns may be seen as the central, prototypical members of the noun class.
1. Four core syntactic functions/ grammatical relations
Huddleston & Pullum, 2005, describe four syntactic functions that may be carried out by phrases headed by nouns (including phrases consisting of just one word). Within the clause they function freely as Subjects, Objects and Predicative Complements. Within Preposition Phrase structure they occur freely as Complements. This fact is one aspect of nouns that is shared by all the subcategories of noun. Here are some examples with the common noun dog:
If the word being investigated has one of these functions, or is the head of a phrase carrying out one of these functions then there is a good chance that it is a noun. Notice though, that all of these functions or syntactic roles may be carried out by other words or types of phrase. So having one of these functions is in no way a guarantee of nounship. For example, verbs, finite and non-finite clauses also frequently occur as Subjects:
A good question at this point might be: why does smoking count as a verb and not a noun here? The answer is that although it is in Subject function, it still retains the syntactic properties of being (a non-finite form of) a verb. For example, this verb can still take a Direct Object:
It can still take a preposition phrase as a Modifier or Adjunct (read adverbial) like other verbs:
It can take an adverb as modifier:
It is clear then that if we are to bother to have parts of speech these need to be separated out from the syntactic role or function that a word may have in a phrase or sentence. (We'll do a more thorough investigation of a case study at the end of the post.)
The syntactic role that a word has may be more or less important depending on what categories are contenders for the word. So for example, adjectives commonly function as Predicative Complements, so if the contending word is in Predicative Complement function, and we are wondering if it's an adjective or a noun, this is not much use to us. However, if we're wondering whether an item is an adverb or a noun, then the fact that the word is a Predicative Complement would be fairly decisive in showing it is a noun. Adverbs generally can't function as Predicative Complements:
2. Other syntactic roles of common nouns
The prototypical functions described above apply to the whole class of nouns. Common nouns however have other syntactic roles that they often take. In particular nouns in English, as well as appearing as the Heads of Noun Phrases, can also be Modifiers within the Noun Phrase structure.
To illustrate, take any item that may have a wrapper, for example biscuits. We can freely generate the compound noun biscuit wrapper. Now if some mad people start collecting these, they will be biscuit wrapper collectors, where the compound noun biscuit wrapper is modifying collectors. If there were enough of them, these people might form a biscuit wrapper collectors association where you could be a Biscuit Wrapper Collectors Association member, a disgruntled one of whom might leave and become a Biscuit Wrapper Collectors Association member assassinator. You get the picture. Just in the same way that both adjectives and nouns can be Predicative Complements, they both freely function as Modifiers within Noun Phrases. If a word cannot be freely used to modify a common noun, then this word is almost definitely not a common noun (pronouns do not freely modify other nouns, nor are they freely modifiable by other nouns).
Nouns and noun phrases also occur much less freely in other types of syntactic roles. So for example, in the following sentence, the noun phrase every three weeks functions as Adjunct of the verb phrase (I use Huddleston & Pullum's terminology here, where ᴀᴅᴊᴜɴᴄᴛ is a special term for a modifier of a verb phrase. Other grammars use the term Adjunct in the same way that the term ᴍᴏᴅɪғɪᴇʀ is used here, namely for an item which is syntactically extra within any given phrase structure):
The phrase every three weeks here is a Noun Phrase. The head of this phrase is the noun weeks. Although this phrase is an Adjunct, there are no grounds for considering it an Adverb Phrase, nor for considering weeks an adverb. The word weeks here retains all of the properties of nouns discussed elsewhere in this piece. It is this fact that makes it a noun. So, the point here is that although the occurrence of nouns as Adjuncts in Verb Phrases is quite restricted, being an Adjunct does not prevent a word from being a noun, although it may make it statistically less likely to be one.
There are many other functions that nouns can have. For example they can be Modifiers in preposition phrases:
I will not attempt to give a definitive list here - if such a list even exists. Suffice it to say, that if a word has a syntactic role that is known to be performed by nouns, then in order to determine the word class of the item, we need to compare the ability of rival word classes to fulfill that role , and look at other criteria too.
3. Modification
Nouns are prototypically modified by adjectives, but as has been shown they are also very commonly modified by other nouns. However, nouns are rarely if ever modified by adverbs. In the very rare instances where they are, the adverb must necessarily come after the noun and not before it:
If a word is modifiable by an adjective, and not by an adverb then it is very, very likely to be a noun. Adverbs can modify many other types of words and phrase, but they are excluded from pre-modifying nouns.
Nouns are frequently post-modified by other phrases, notably preposition phrases, relative clauses and adjective phrases.
4. Complementation
Many nouns take various complements, such as finite clauses and preposition phrases:
However, Huddleston & Pullum note that:
... nouns differ from verbs and prepositions in that they do not take objects: I dislike it, but not * my dislike it. (p. 326)
This is one of the factors that rules out smoking from being a noun in the examples further above.
5. Determiners
Certain words occur nearly exclusively in Determinative function in noun phrases. These external dependents of the noun are a good indication of a word being a noun. Here are some examples:
The determiner this in the example above shows that this is the noun patient and not the homonymous adjective. The word every here is a near cast iron guarantee that the word opportunity is a noun. However, not all determiners are as good as others for this job. In particular, the can occur in Determinative function in phrases that have no noun:
Here we see the occurring with adjectives. Notice that every cannot be used in these ways.
6. Inflection for number
Common nouns usually inflect for number and for case. Typically, plurally inflected nouns take /s/ or /z/ as a suffix represented in the writing by the letter 'S'. If we see a word which seems to have an 'S ending because it is plural, this is a strong indication that the item is a noun. If a word doesn't inflect for number then this may be a sign that it is not a noun. However, we need to be a bit careful. There are many irregular plurals in English:
There are also nouns which are the same in the singular or plural:
There are also nouns that end in an 'S' whether they are singular or plural:
There are also nouns that only occur in the plural:
There are nouns that only occur in the singular, or are uncountable:
What this shows is that the ability for a word to show singular and plural forms with 'S' is useful, but a lack of inflection, or of regular inflection, is not sufficient reason to exclude an item from being a noun.
7. Inflection for case
Common nouns inflect for case. They have two forms. The uninflected form is often called PLAIN CASE. The other case is GENITIVE. The genitive form involves the suffix/clitic /s/ or /z/, represented in the writing as 'S' used in conjunction with an apostrophe:
We need to be a little careful here. First of all, this clitic actually gets appended to noun phrases, not just nouns:
Here we see this clitic appearing after the noun phrase the woman you like. We should not infer from the writing that like is a noun here! Secondly some phrases without nouns can also take this clitic:
Here we see the clitic after the phrase the blind. Some writers like Huddleston & Pullum regard the blind here as a noun phrase without a noun. Here we see this clitic attached to an adjective.
8. Negative attributes
Of course, when considering whether a phrase is a noun or some other type of word, it is the properties that another class of words have and that nouns don't, which will provided the decisive data. Importantly, nouns can't function as the head of a main clause. In other words they can't assume the syntactic role of Predicator (the function carried out by the verb).
Another feature of nouns is that they are not gradable, whereas many other adjectives are. Equally it is the property of not being modifiable by adverbs which is crucial for demonstrating that a noun modifying other nouns is still a noun and not an adjective.
There are many other negative criteria we can use to demonstrate that a given word is likely to be or definitely isn't a noun.
9. The pronoun substitution test
It is sometimes posited that a good test to see if an item is a noun is to see whether it can be grammatically replaced with a pronoun. In actual fact, although nouns will often be replaceable with pronouns, more often than not in declarative sentences so will any other phrase in Subject or Object function, or functioning as the Complement of a Preposition:
None of the items that have been replaced by the pronoun it here is a noun. Notice as well, that pronouns don't 'replace' nouns if the noun has dependents. When we substitute a phrase with a pronoun, the entire noun phrase goes, determiners, modifiers and complements too. In addition we cannnot use this test when a noun has the function of Modifier within a phrase including when they are Adjuncts (- modifiers in verb phrases). The nouns and noun phrases in the following examples cannot be replaced by pronouns:
It seems that the pronoun substitution test is of limited value. The item being replaced may not be a noun. Furthermore nouns can often not be replaced at all depending on their syntactic role. If we have to determine the syntactic role before we do the test there is no point doing it. The reason is that the syntactic role will already tell us how likely an item is to be a noun with the same reliability as the pronoun test. This is because in declarative sentences any item in Subject function will be able to be replaced by a pronoun, whether it's a noun or not. So the chances of the word being replaceable by a pronoun are the same as the chances of the word being a Subject. Neither of these is a guarantee of nounship. The syntactic role that an item has in a given sentence is very rarely a definitive indication of the category of a word. The reason is, of course, that all syntactic roles apart from Predicator may be carried out by more than one type of word or phrase.
A trivial point, a red herring
There are of course some words which sound and are spelt the same. This includes words whose meaning is radically different, as well as words with very similar meanings which belong to different parts of speech. It is common in linguistics to talk about lexemes. We require the notion of a lexeme to indicate that words like liked and liking are versions of the same entity, namely they are inflections of the verb like. So liked and liking are instantiations of the same lexeme.
However, we would not say that man in man of the match and man the decks are instantiations of the same lexeme, even though they may look and sound identical. The reason is that the first is an instance of the noun man whereas the second is an instance of the verb. Because we consider them as instantiations of different lexemes with the same sound and the same spelling, these words are considered homonyms. Although they have some semantic similarities, they represent different types of concept. Also syntactically, the noun man belongs with other instantiations of the noun such as man's, men and men's, whereas the verb belongs with mans, manning, manned and the present tense form man.
So what does this have to do with the question here? Well, it is often said that the category of a word depends on how it used in a sentence. Now if "word" here means a particular series of sounds or a group of letters, then this is trivially, but maybe interestingly, true. We can only understand whether a group of letters represents the noun lexeme man or the verb lexeme man, for example by seeing this group of letters in context.
However, there's another, very harmful and unprincipled idea which sounds very similar, which is that a word should be assigned its part of speech according to what syntactic role, or grammatical function it has in a particular sentence. People who have this kind of idea say things like:
The problem with this type of theory is that it works on the schoolkid assumption that syntactic roles belong to specific word categories. This is because, sadly, the teaching of grammar in schools is of particularly poor quality. Most people are taught at school that words that describe nouns are adjectives, words that describe verbs are adverbs, nouns represent things and verbs represent actions. None of this of course is true.
Here is what Geoffrey Pullum has to say about this problem. The quote is taken from LEXICAL CATEGORIZATION IN ENGLISH DICTIONARIES AND TRADITIONAL GRAMMARS 2009:
Most of the deepest blunders in English grammar as traditionally presented over the past two or three centuries stem from a single long-standing confusion between (i) grammatical categories or word classes; (ii) syntactic functions or grammatical relations; and (iii) semantic and discourse-related notions.
It is surprising to see the tenacity of this confusion. It does not appear in other domains. People do not confuse butter knives with screwdrivers, even though occasionally someone who cannot find a screwdriver may use a butter knife to turn a screw. Yet in grammar people just cannot keep syntactically relevant categories or classes of words separate from the relational properties they have when used in particular constructions, and cannot keep either separate from meaning. They insist on trying to define the first of these in terms of the other two, and they have done so since the very earliest attempts to write grammars of English.
What this means is that we should be able to distinguish between the fact that something modifies a noun and the fact that it is a particular part of speech. Additionally, ideas such as "this word tells us when something happened, so it is an adverb" or even worse "this word tells us when something happened, so it is being used as an adverb" are severely misguided. Neither the semantic content of an item, nor its syntactic role are defining characteristics of its part of speech.
Case Studies
Probably the easiest way to understand how we might run various tests to check the noun status of an item, is to look at these tests in action. There are (or will be shortly) two case studies of particular words in a different post here.
A noun generally takes an article ("the"), can be modified by an adjective, cannot be modified by an adverb, cannot take a direct object.
To illustrate, here is a sort of minimal pair between noun and verb: "Eating lobster is forbidden." (This is the first half of the pair.) The subject noun phrase, "eating lobster", has "eating" as its head, so you might suspect that "eating" is a noun. Yet it isn't -- "eating" here is a verb, which you can tell from the fact that it takes the direct object "lobster". Nouns can't have direct objects in English.
In addition, in the example, "eating" cannot be preceded by an article: *"The eating lobster is forbidden" is bad (but note below). If "eating" were a noun, "the"/"a" should be okay.
Also, if "eating" were a noun, it could not be modified by an adverb, yet here, we get "Eating lobster rapidly is forbidden", and if it were a noun, it could be modified by an adjective, but here: *"Rapid eating lobster is forbidden." You can't modify "eating" with the adjective "rapid", because "eating" isn't a noun.
However, if we change the example by removing the direct object, we get the second half of the minimal pair: "The eating of lobster is forbidden." Now, "eating" is a noun. Note the preceding article "the", which is one sign that we're dealing with a noun.
If it's a noun, it ought not to be possible to modify it with an adverb, and it isn't possible: *"The rapidly eating of lobster is forbidden." But it should be possible to modify the noun by an adjective, and it is: "The rapid eating of lobster is forbidden."
Notice that all these methods for distinguishing a noun from a verb are consistent with each other.
Note about the grammaticality of "The eating lobster is forbidden": There may be a grammatical sense of this in which "lobster" is the head noun of the subject and "eating" is a modifier of that noun, but then, of course, "eating" is still not a noun.
One simple feature of a noun is that it can be replaced by "he/she/it" when it is a single noun in singular and by "they" when it is a single noun in plural. I have never tested if this feature really helps in difficult cases, as in English a noun can also be a verb (a cry, to cry), an adjective (the dark, a dark corner) or even an adverb (my home, to go home). Sometimes, I think, the use of the word in a sentence is decisive.
Case Study: Weekdays
It's probably easiest to get a handle on what some tests for noun status might look like, by seeing one in action. Let's have a look at the item weekdays in a sentence such as:
The three primary competing word categories for this word are probably adverb, noun and preposition. For want of space, we will just look at the noun and adverb options.
Syntactic function
This phrase is an Adjunct (read adverbial) in the clause structure. It's modifying the verb phrase is open. It's an adjunct because the phrase is not necessary for the sentence to be well formed. The sentence It's open is grammatical without this extra phrase. This syntactic function is associated in school-learned grammar with adverbs. Of course, preposition phrases very often carry out this function too. Just in terms of statistical probability, the fact this is an adjunct makes it statistically more likely to be an adverb than a noun.
However, this phrase is, more specifically, a temporal adjunct. We have seen that noun phrases very often function as temporal adjuncts. Here are some examples:
In accordance with its grammatical relations within this particular sentence, it is perfectly possible, therefore, that weekdays is a noun heading its own Noun Phrase.
Let's look at more data from syntactic functions. If weekdays is a noun, it should be able to function freely as an NP as a Subject, Object or Predicative Complement:
If weekdays is an adverb we would expect ungrammatical results when used as a Predicative complement:
We see above the bad results from the adverb regularly when used as a Predicative complement. In contrast weekdays seems fine.
Lastly in terms of syntactic function, if weekdays is a common noun we would expect it to be able to occur in as Modifier of another noun. If it is an adverb then pre-modification of another noun should be ungrammatical:
It we assume that weekdays is a plural noun then we would expect the singular form to be used as a modifier even more freely:
The examples above are all grammatical. Compare these with:
These examples with adverbs, in contrast, are all ungrammatical. This more or less rules out weekdays from being an adverb and provides strong evidence for it being a noun.
Modification
If weekdays is a noun, we expect it to be modifiable by other nouns and by adjectives as well. We do not expect it to be modifiable by adverbs. If it is an adverb we expect it to be modifiable by other adverbs. We don't expect it to be modifiable by adjectives:
The examples above show grammatical results for modification by adjectives and nouns and bad result for modification by adverbs. This again shows that weekdays is almost definitely a noun, not an adverb.
Determiners
If weekdays is a noun, we should be able to use it with determiners such as every, some, these, the and so forth. We will save the singular determiner every till we consider whether weekdays is a plural form in the next section. Here are examples with some other determiners:
Adverbs don't take determiners. The data above constitutes virtually cast iron proof that weekdays is a noun here.
Plural inflections
If weekdays is a noun, it's probably plural given the 'S' ending. We have already seen it in a singular form modifying other nouns further above. When we see it functioning as head of its own NP, it will need a determiner. Below we see it with the determiners every and one:
This occurrence of weekday with the determiner every is a near cast iron guarantee of nounship. The determiner every only occurs as a dependent in noun phrases headed by nouns.
Genitive inflection
We can find instances of genitively inflected weekday's in examples such as:
Again adverbs and adverb phrases do not have genitively inflected forms.
Other Morphology
The morphology of weekdays also strongly suggests that it is a noun rather than an adverb. Weekdays lacks the -ly suffix that adverbs in English typically possess. Furthermore it appears to be a compound made from two nouns, week and day(s). Most noun noun compounds in English are nouns. A few also occur as verbs (to railroad someone). Virtually none occur as adverbs.
A complete lack of adverb properties
In addition to the evidence above weekdays shows none of the properties we should expect from adverbs. We have already mentioned that it has non adverb-like morphology and that unlike adverbs weekdays can occur as a predicative complement. In addition weekdays has no comparative forms and does not enter into comparative constructions. It cannot be modified by the kinds of adverbs which we see freely modifying other adverbs:
so regularly
so beautifully
so soon
*so weekdays
or:
quite regularly
quite beautifully
quite soon
*quite weekdays
Conclusion.
The word weekdays is a noun, not an adverb.
Its internal morphology suggests it is a noun.
The phrases it heads can fulfill the syntactic functions that are typical of temporal noun phrases: Subject, Object, Predicative Complement and Adjunct.
As with other common nouns, it can function as a modifier in a noun phrase.
It can be modified by other nouns and by adjectives.
It cannot be modified by adverbs.
It has both a singular form and a regular plural form.
It has a genitively inflected form.
It can occur with a large range of determiners, most importantly with the determiner every.
The strongest evidence here is the fact that it has a plural form and that it can occur with the determiner every. However, all the evidence above clearly demonstrates that weekdays is a noun. It is not a noun with adverb-like properties. It is a bona fide 100% common garden variety noun with no adverb-like properties whatsoever.
There is no consensus among linguists on how the parts of speech issue is best handled for the trickier cases.
Bas Aarts, in The Handbook of English Linguistics 2006 (ed Aarts & McMahon): English Word Classes and Phrases (Aarts & Haegeman): 2.3 Word class boundaries and gradience gives the analyses of three opposing schools [the extract below is modified].
We could approach ... [the examples given are for ing-form usages] in at least three ways:
Firstly, we could say that verbs and nouns are on a cline or gradient, such that these word classes shade into each other gradually.
Another possibility is to say that [the word in question in its usage in an actual example] is a hybrid element and belongs to the classes [here verb and noun] at the same time. This strategy is adopted in cognitive approaches to grammar. It is also proposed [by] Hudson (2003).
A third possible strategy would be to retain the [traditional/fairytale?] sharp boundaries between the [here] verb and noun categories, and say that though V-ing in sentence A has verbal as well as nominal properties, the verbal ones outweigh the nominal ones.... [And who gets to decide this!?]
Testing for nouns and verbs say is not like doing an A-level chemistry inorganic analysis on a mixture of salts. There, it's indisputable that there is a single correct answer; the single problem the candidates have is to apply the tests correctly. With parts of speech, the periodic table hasn't been agreed upon.
I'm English and so a native English speaker, and I consider that in 95+% of cases I can pronounce with certainty both on the grammatical and semantic correctness of an English utterance, although I could not with much certainty identify all of the grammatical terms of the utterance. The answers given here are fascinating and eye-opening when I see that identifying what most English speakers probably think of as the most easily identifiable grammatical term, the noun, as, in a significant(?) number of cases, not so identifiable. And if such is the case for the noun then god help ordinary mortals when it comes to unambiguously identifying other grammatical terms.
It is just recently that I have been looking into the grammar of English because I intend to take a CELTA course, with the intention of teaching English to non-native speakers. As preparation I looked around the web for rules to answer questions about grammar such as is posed initially here, and I found advice on determining a noun by a test of three parts: can the word take "the" or "a"; can it be pluralised; and can it be modified by an adjective. I tried many cases with success until I came upon the sentence "It's at five o'clock.". Having difficulty in identifying the term "five o'clock", I compared this with sentences such as "It's at the races", applied the test to the "the races" and concluded that "the races" is a noun; hence "five o'clock" must be a noun, but it doesn't pass any of the tests. I then tried to find a site that could declare what grammatical term "five o'clock" is, and in Wiktionary it is declared as a noun.
So, if "five o'clock" is a noun then the triple test can't be trusted. Hence, there is no simple test for a noun, and probably for other grammatical terms, as the replies here to the original question indicate. Thus, if I get the CELTA certification and subsequently start to pontificate on the identity of English grammatical terms to non-native English learners (or even to native ones), I can imagine that some of the time I'll be skating on a razor's edge, having to learn to deflect and postpone some questions of English grammar until I can consult more learned sources.
