Here's why:
* Prepositional phrases: "For" is typically used as a preposition, introducing a prepositional phrase that modifies a noun or verb. Ending a sentence with "for" can leave the reader wondering what the prepositional phrase is modifying.
* Clarity and flow: Ending with "for" can sometimes create a less clear and natural flow in a sentence.
Examples:
* Informal: "I'm going to the store for." (This leaves the reader wondering what you're going to the store *for*.)
* Formal: "I'm going to the store for groceries." (This is clearer and more natural.)
Exceptions:
* Questions: Ending with "for" is perfectly acceptable in questions, such as "What is this for?"
* Informal contexts: In casual conversation or informal writing, ending with "for" is perfectly fine.
In general, try to avoid ending sentences with "for" in formal writing. It's often best to rephrase the sentence to make it clearer and more grammatically sound.