The keyword term "September 11th of 2001" functions grammatically as a proper noun phrase. As a complete unit, it names a specific and unique calendar date. Like other proper nouns (e.g., "World War II," "the Renaissance"), it identifies a singular, capitalized entity rather than a general class of things. This classification as a noun is its primary and most fundamental grammatical identity.
While its core identity is a noun phrase, its syntactic function can vary depending on its placement within a sentence. It can act as the subject ("September 11th of 2001 changed global politics"), the object of a preposition ("Reflections on the period after September 11th of 2001..."), or a predicate nominative ("The date in question was September 11th of 2001"). Furthermore, this noun phrase is frequently used as an adjectival modifier, also known as a noun adjunct, to describe another noun (e.g., "the September 11th of 2001 attacks"). It can also function as an adverbial phrase of time, answering the question "when?" (e.g., "The tragedy occurred September 11th of 2001.").
For the purpose of analysis, recognizing its primary role as a proper noun phrase is crucial. This establishes the term not just as a point in time, but as a named event with a distinct identity. This nominal status is what allows the phrase to carry significant semantic weight and to be deployed flexibly as an adjectival or adverbial concept. Therefore, the main point of its grammatical function is its identity as a proper noun, which encapsulates the historical, cultural, and political significance of the event it names.
