The keyword "September 11th, 2001" functions grammatically as a proper noun. As a specific designation for a particular calendar date, it names a unique entity, which is the defining characteristic of a proper noun.
While its fundamental classification is a proper noun, the phrase can also function as an adjective depending on its syntactic role. When used as the subject of a sentence ("September 11th, 2001, is a date of historical significance") or the object of a preposition ("The commission investigated events leading up to September 11th, 2001"), it acts as a noun. However, when it modifies another noun ("the September 11th, 2001, attacks"), it functions as an adjectival phrase, specifying the noun it describes.
For the purpose of establishing a primary classification as a main point, "proper noun" is the definitive part of speech for the phrase itself. Its adjectival use is a functional shift determined by its context within a sentence. Recognizing that the term is fundamentally a proper noun is the crucial step for ensuring grammatical precision and clarity in the article.
