The core component of the keyword phrase, "September 11th," functions as a proper noun. It is the specific name of a calendar date that has come to signify a major historical event. The additional words "on this day" form a prepositional phrase that acts adverbially, modifying the implied action of searching or discussing by specifying the temporal context. Therefore, the grammatical subject and main point of the phrase is the proper noun.
A proper noun is a name used for an individual entity, distinguished from a common noun, which refers to a general class of entities. While "day" is a common noun, "September 11th" is the specific name of one particular day, and its capitalization reflects this status. Due to the events of 2001, this proper noun has acquired a distinct and powerful connotation, functioning as a unique identifier for the terrorist attacks on the United States. In linguistic terms, it has become a synecdoche, where the date itself represents the entirety of the events, their consequences, and their ongoing historical significance.
Identifying "September 11th" as the main-point proper noun is crucial because it defines the article's subject as a singular, specific topic. This grammatical classification mandates that the content must focus on the unique attributes and history associated with that name, rather than on general concepts. It establishes that the article is not about the eleventh day of a month in general, but about the specific entity known as "September 11th." This focus ensures thematic coherence and directs the research and writing process toward historical fact, commemoration, and analysis directly linked to that specific name.
