Here's why:
* Prepositions show the relationship between a noun or pronoun and another word in the sentence. They often indicate location, direction, time, or manner. Examples include "on," "in," "at," "to," "from," "with," "by," etc.
* "But" is a coordinating conjunction. It joins words, phrases, or clauses of equal grammatical rank, often to express contrast or opposition.
Example:
* Preposition: "I walked to the store." ("to" shows the direction of the walk)
* Conjunction: "I wanted pizza, but they only had burgers." ("but" connects two contrasting ideas)
Let me know if you have any other grammar questions!