Here's why:
* Preposition: When "except" is used as a preposition, it indicates exclusion and is followed by a noun or pronoun. Example: "Everyone came to the party except John."
* Coordinating Conjunction: When "except" is used as a coordinating conjunction, it connects two clauses, much like "but" does. It indicates a contrast or exception to the first clause. Example: "I like all kinds of food, except spicy food."
In this second example, "except" could be replaced with "but," making it clear that it functions as a conjunction.
Let me know if you'd like to explore other examples!