The phrase "how long until september 11 2025" is grammatically classified as an interrogative phrase. It is not a single part of speech but a construction of multiple components working in unison to form a question. The core elements are an adverbial phrase ("how long"), a preposition ("until"), and a noun phrase ("september 11 2025"), which collectively function to seek information about a duration of time.
A detailed grammatical analysis identifies the specific role of each component. The term "how long" is an interrogative adverbial phrase of duration, modifying an implied verb (such as "is it") to ask about a quantity of time. The word "until" is a preposition that establishes a temporal boundary or endpoint for that duration. The specific date, "september 11 2025," is a proper noun phrase that acts as the object of the preposition "until." The entire prepositional phrase "until september 11 2025" functions adverbially, specifying the target point in time.
In its practical application, this structure is a direct inquiry designed to elicit a quantitative answer, such as a specific number of days, months, or years. The combination of an interrogative adverb, a preposition, and a noun phrase creates a complete and coherent question about the temporal interval between the present and a specified future date. Therefore, its primary grammatical function is to serve as an inquiry, making "interrogative phrase" its most accurate classification.
