Here's why:
* Prepositions show relationships: Prepositions show the relationship between a noun or pronoun (called the object of the preposition) and another word in the sentence. For example: "The book is on the table." "On" shows the location of the book.
* Nouns are the names of things: Nouns are the words that represent people, places, things, and ideas. They are the core of a sentence.
* Prepositions require objects: Prepositions need an object to complete their meaning. The object is usually a noun or pronoun.
Think of it this way:
* Nouns are the "what" of a sentence (e.g., "the book").
* Prepositions are the "how" or "where" of a sentence (e.g., "on").
Let me know if you have any other questions!