The keyword phrase "september 11th day" functions grammatically as a noun phrase. The core or head of this phrase is the noun "day." The words preceding it, "september 11th," act as a compound modifier specifying which particular day is being referenced.
In a detailed grammatical analysis, the word "day" is the central noun. The phrase "september 11th" operates as an adjectival phrase modifying "day." This adjectival phrase itself is composed of "September," a proper noun used adjectivally to name the month, and "11th," an ordinal number that specifies the date. Together, they form a single descriptive unit that narrows the general concept of "day" to a unique, specific instance.
For the purpose of an article, recognizing this structure is crucial. Treating "september 11th day" as a noun phrase allows it to function as a subject (e.g., "The September 11th day changed history"), an object (e.g., "We will always remember the September 11th day"), or the object of a preposition. The adjectival function of "September 11th" is the key to its descriptive power, attaching a wealth of specific historical and cultural significance to the simple noun "day."
