An (One) article is an adjective.
The (Three) articles are adjectives.
Article without an article is just another noun.
"Conjunction Junction, what's your function? Hooking up words and phrases and clauses. Conjunction Junction, what's their function? I've got 'and,' 'but,' and 'or,' they'll get you pretty far..."
If you don't have a song for it, it's not a part of speech. Sorry. That's the rule.