The Question of Conversion or Ellipsis

Yesterday during syntax class, I came across an interesting question that I elaborated later on with my professor. It was the question whether the words “sick” and “poor” in phrases like “The sick do this and that” or “The poor are so and so” are adjectives or nouns. It seems there is some disagreement on this topic. The theory my professor brought forth was that the noun is omitted, thus the words in questions are still adjectives and the noun is thought, but not written or spoken. I have to admit, it was the first time that I heard this theory, but I still gave it some thought and checked it against my own theory (which is also the one I learnt in school, but that doesn’t need to mean it’s right).

So, my own theory is that those words are nouns which were derived from the adjectives via zero-derivation/conversion.

There are several indications that lead me to assume my theory is more accurate (and I’m open to discussion in the comments section). First, and this is the rule I learnt at school, we would need the pronoun “one” or “ones” to replace the omitted noun if the words in question were still adjectives. With the (granted, still limited) linguistic knowledge I have by now, I can even explain this rule according to current constituent theory. “The poor” is a DP (determiner phrase) because it is headed by the determiner “the”. A DP takes an NP (noun phrase) as complement. Now, if “poor” were an adjective, as claimed by the ellipsis theory, we would have an NP without a noun, which is not possible. Therefore, the pronoun “one” or “ones” is inserted to fill the head position in the NP.

One might argue that the noun is still “there”, just not explicit, since you can also omit verbs in certain cases without losing their meaning. OK, let’s have a look at this point. The verb can be omitted in a phrase like “I haven’t been to Ireland, and never will”. What is omitted here is “be to Ireland”, but even with the omission, the sentence still has the same meaning. So what exactly did we omit here? In order to be a valid argument for the ellipsis theory above, it has to be the head of a phrase. “be to Ireland” is a VP (verb phrase). What about “will”? It actually doesn’t belong to the VP but instead fills the position I in the IP (inflection phrase). So we omit a complete VP in the example sentence, not just the head of a phrase.

Therefore, my argumentation leads me to assume that “sick” and “poor” in the above cases are indeed nouns derived from the corresponding adjectives since linguistic analysis points to the assumption that they are, indeed, heads of their respective NPs.

What do you think? Let me know in the comments section; I’m most definitely open to linguistic debate (as long as everyone stays calm).