The keyword phrase "September 11, 2001" primarily functions as a proper noun. As a specific date, it names a unique point in time, much like a name identifies a specific person or place. This grammatical classification is foundational because it treats the date as a singular, identifiable entity, which is central to its historical significance.
In addition to its role as a proper noun, the phrase is frequently used as an adjective, more specifically a noun adjunct. In this capacity, it modifies another noun to specify a direct connection to the events of that day. For example, in the phrase "the September 11, 2001 attacks," the date functions adjectivally to describe which attacks are being referenced. This dual functionality is key; when the date stands alone as the subject or object in a sentence (e.g., "The world was altered by September 11, 2001"), it is a noun. When it describes another noun (e.g., "the post-September 11, 2001 era"), it is an adjective.
For the purpose of writing an article, recognizing this distinction is crucial for achieving syntactical precision and clarity. The primary identity of "September 11, 2001" is a proper noun, establishing the event itself as the core subject. Its secondary, adjectival use allows for the exploration of related concepts, policies, and consequences that are defined by their relationship to the event. The choice between these grammatical functions will depend on whether the article is discussing the day itself or the attributes of things associated with it.
