* Sentences need a subject and a verb. A prepositional phrase consists of a preposition (like "on," "in," "with," "to") followed by its object (a noun or pronoun). It doesn't have a subject or a verb.
* Prepositional phrases modify other words. They act as adjectives or adverbs, providing information about nouns or verbs.
Example:
* Incorrect: "In the park." (This is a prepositional phrase, lacking a subject and verb)
* Correct: "The children played in the park." (This is a complete sentence with a subject, "children," and a verb, "played.")
In summary, a prepositional phrase is a part of a sentence, not a complete sentence itself.