* Adverb: When "next" indicates sequence or order, it acts as an adverb.
* Example: "First, we'll eat. Next, we'll play games."
* Adjective: When "next" refers to the following item in a series, it acts as an adjective.
* Example: "The next chapter is about the hero's escape."
* Preposition: When "next to" is used to show proximity, it acts as a preposition.
* Example: "The cat sat next to the dog."
So, to determine the part of speech, consider its function in the sentence.