Traditionally, a is regarded as a determinative. Traditionally, any is considered a determinative when used with a following noun and either a determinative or a pronoun when used on its own, depending on which grammar one subscribes to. However, it can be argued that such analyses have got it wrong. (That isn't my own view)
Strange though it may seem, there are very good reasons for arguing that words like a and the are the same type of word as you or we. However, it is important to understand that these are not traditional analyses.
This looks like a simple cut and dried question. It might even seem trivially simple. However, far from it, it is a rivetingly interesting problem, and one that has been much discussed in the literature.
Before we can get going we need to have a look at the anatomy of noun phrases. Most grammars of English recognise that noun phrases are comprised of two smaller chunks or phrases. Consider the following noun phrase:
Here we can divide the phrase into the chunk the and then the second part, slimy dinosaur. This reflects the fact that slimy dinosaur seems to have a coherence that the slimy doesn't.
Just as we see special names for the jobs done within a clause, for example Subject or Object, the jobs that different parts of a noun phrase carry out can also can be given similar titles. Words or phrases that appear as the first chunk, such as the word the in the example above, do the job of Determiner. The chunks that come after them, that contain the main noun, can be referred to as Heads.
Now, in many grammars, in the same way that Subjects are very frequently nouns or noun phrases, Determiners are frequently determinatives. Determinatives are commonly thought to be words such as the, some, any and so forth. However, just in the same way that Subjects are not always noun phrases, but may be clauses, adjective phrases and so forth, Determiners are not always determinatives. Sometimes, the Determiner job may be done by another phrase such as a noun phrase. Consider
- Bob's slimy dinosaur
- That man's slimy dinosaur
In the examples above, the Determiners are the noun phrases Bob's and That man's respectively. They aren't determinatives. Ok, so back to the Original Poster's question.
Modern and traditional grammars: any
Let's start with the word any. Typically, this word occurs on the left edge of noun phrases:
- I couldn't find any new books.
- I couldn't find any.
In most twentieth century grammars, the word any would have been regarded as a determinative in (1) where it occurs to the left of the chunk new books. However, it would have been regarded as a pronoun in (2) where there is no following word or phrase.
Now, this seems a bit odd, because the word any seems to mean exactly the same thing in both examples. Notice that the verb know is still regarded as a verb in the following examples:
- I know that Bob left.
- I know.
In most twenty-first century grammars, the word any is treated as a determinative in both (1) and (2) above. We might want to construe those sentences like this:
- I could find [any new books]
- I couldn't find [any
Just as we could construe the know examples like this:
- I [know that Bob left]
- I [know
that Bob left]
The fact that there are no following words does not mean that the preceding word has a different part of speech in each case.
Modern and traditional grammars a(n)
In most modern and traditional grammars, the words a and the are termed articles. These are usually considered a subcategory of the determinatives. Along with the word every, these determinatives cannot appear without a following phrase:
- Can I have a book?
- *Can I have a? (ungrammatical)
- Can I have the book?
- *Can I have the? (ungrammatical)
Compare those with:
- Can I have any custard?
- Can I have any?
- Can I have that book?
- Can I have that?
Here we see that the determinatives any and that can occur with or without a following word or phrase.
Now for the interesting bit
OK, so far so good. However, we touched upon a problem just now that hasn't been properly addressed. We looked at the verb know and saw that it could take a clause or occur without one. Of course, it can occur with a following noun phrase as well. This throws up some problems with the accounts given above.
In any description of a language it is useful to differentiate the jobs done within a clause or phrase, for example Subject or Determiner, with the type of word or phrase carrying out that job, for example a noun, adjective, verb (or noun phrase, adjective phrase or verb phrase).
Writers like Abney (1987), Hudson (2000) and Spinillo (2004) have argued that many of the words that are taken to be determintives are actually different types of word that happen to appear in Determiner function. So, for example, Spinillo argues that many is an adjective, not a deteminative. There are several reasons why this is most likely the case. Determinatives cannot occur as ascriptive Predicative Complements, where as adjectives can:
- Our objections were numerous.
- Our objections were many.
- *Our objections were some. (ungrammatical)
- *Our objections were any. (ungrammatical)
Determinatives cannot iterate, whilst adjectives can:
- blue, blue eyes
- many, many eyes
- *the, the eyes (ungrammatical)
- *some, some eyes (ungrammatical)
Certain types of adjectives can occur before entire noun phrases. Typical 'determinatives' cannot:
- bigger a problem
- many a problem
- *this a problem (ungrammatical)
- *some a problem (ungrammatical)
Generally, adjectives are likely to be gradeable, traditional typical determinatives are not:
- good people / better people / best people
- many people / more people / most people
- some people / *somer people /*somest people (non-existent)
Lastly (but only because of time constraints), adjectives are regularly modifiable by degree adverbs such as so and how whereas proptotypical determinatives aren't:
- so big
- how big?
- so many
- how many?
- *so some (ungrammatical)
- *how some? (ungrammatical)
Most, but not all, of the above is from Spinillo (see references). In this kind of way many determinatives can be dispatched to either the adjective or noun categories, to leave a much small number of central items. These words are nearly all monosyllabic. They don't iterate, aren't easily modifiable by adjectives, cannot occur with other similar words, don't occur as ascriptive predicative complements, have little or no internal morphology, are high frequency, occur in initial position in noun phrases.
These qualities are all also ones observed in the pronoun category. As we have already seen, most so-called determinatives can occur without a following noun just like pronouns - which is the main reason that they have been categorised as pronouns when doing so. The argument that determinatives and pronouns are actually the same type of word would be stronger if prototypical pronouns could also function in the same way as determinatives.
Now consider the following:
- We band of brothers
- You bastards
- Them idiots (in several non-standard dialects)
Here we see words that are commonly held to be pronouns occurring in Determiner function. We can compare these with traditional determinatives:
- We band of brothers will never leave
- We will never leave
- This spot will never disappear.
- This will never disappear.
- You bastards always annoy me.
- You always annoy me.
- Some members will come
- Some will come
Here we see 'pronouns' behaving like prototypical 'determinatives' and 'determinatives' behaving like prototypical 'pronouns'.
The final move
Above we saw that we always count verbs as verbs regardless of whether they occur before clauses or noun phrases. If we treat determinatives/pronouns in the same way, then we have some that occur with an optional following noun phrase (this, some, we etc), some which cannot occur with a following noun phrase (I, they etc) and then finally some that must occur with a following noun phrase (every, the, a). This would mirror the behaviour of other types of word, such as verbs, which can be optionally transitive, always transitive or always intransitive.
This type of analysis, of course, raises many other questions. For example, are these words best analysed as all determinatives' or all 'pronouns' - and if they are pronouns, are they a subcategory of noun? It also calls into question whether it is the determinative or the common noun which is the head of the phrases that we traditionally regard as noun phrases.
Writers like Dick Hudson argue that these words, including the articles, are all pronouns - in which case, as the Original Poster intuitively guesses, a is—just like the word any—a pronoun!
[Note that Hudson does explicitly state that the word a is a pronoun, even though it cannot occur on its own]
This slovenly explanation here is wanting on many fronts, largely because of time and space and the author's own failings and general laziness. However, here are some of the most important references if the reader wishes to do any further reading:
- Ben Jonson 1640 The English grammar [The Scholar Press 1972] in which he discusses articles as a subctegory of pronoun
- Steven P Abney 1987 The noun phrase in its sentential aspect MIT Press
- Dick (Richard) Hudson 1997 Syntax without functional categories UCL working papers in linguistics 9 pp. 253-279.
- Mariangela Spinillo 2004 Reconceptualising the English Determiner Class. PhD thesis, University College London.