What part of speech are articles before possessive adjectives?

Question

Today I was diagramming a sentence when I noticed something that confused me. I had a sentence that was basically like this:

A parent's greatest concern is rearing his children correctly.

"Concern" is obviously the noun there, with "parent's" and "greatest" as adjectives modifying it, but what is "a"? It's an article which I thought were always adjectives, but it looks like it's modifying "parent's", which would have to make it an adverb since you can't stack adjectives, right?

What is it? Can articles be adverbs if they're modifying possessive adjectives? Do you just stack adjectives for some reason? Does it somehow modify the subject "concern" for some reason?

Answer 1

A does not modify concern. "A parent's greatest concern" means "The greatest concern of any parent". The A is the determiner signifying a general parent.

Iterums' comment on the question is relevant: it's perfectly possible to have more than one adjective. However, although determiners can be classed as adjectives, "modern theorists of grammar prefer to distinguish determiners as a separate word class from adjectives, which are simple modifiers of nouns, expressing attributes of the thing referred to." (Wikipedia)

A determiner does not express an attribute of the thing referred to. It "serves to express the reference of that noun or noun phrase in the context. That is, a determiner may indicate whether the noun is referring to a definite or indefinite element of a class, to a closer or more distant element, to an element belonging to a specified person or thing, to a particular number or quantity, etc." (Ibid.)