What part of speech is "down" in the phrase "ran down the street"?

In the phrase "ran down the street," "down" functions as a preposition. Prepositions are words that show relationships between other words in a sentence, often indicating direction, location, or time. Here, "down" indicates the direction of the action of running. In this context, it connects "ran" (the verb) to "the street" (the noun phrase), helping to clarify where the action is taking place.

While "down" can sometimes serve as an adverb in other contexts, in this specific instance, it is establishing a relationship with the noun "street," which confirms its role as a preposition. Other parts of speech, such as nouns and adjectives, do not fit this context since neither would appropriately convey the directional aspect required in this sentence.