The prescriptive rule "don't end sentences with prepositions" is often taught, but linguistically, English grammar naturally allows prepositions at the end of sentences: "What are you looking for?" (not the awkward "For what are you looking?"). Preposition stranding is grammatically correct in modern English, especially in questions and relative clauses.
Recognize that ending sentences with prepositions is acceptable in modern English, especially in informal contexts and questions. When writing formally, be aware of this traditional rule but understand that following it sometimes creates unnatural constructions.
You already know that prepositional phrases attach to nouns or verbs to add information about location, direction, time, or relationships: "She talked *to the manager*," "He looked *at the painting*." In these examples, the preposition and its object stay together as a unit. Preposition stranding is what happens when the object of the preposition moves elsewhere in the sentence — to the front, or out entirely — leaving the preposition behind at the end: "Who did she talk *to*?" "That's the painting he looked *at*."
The rule against ending sentences with prepositions is one of the most famous prescriptive rules in English — and one of the least grounded in how English actually works. It was invented in the 17th century by grammarians like John Dryden, who modeled their prescriptions on Latin. Latin cannot strand prepositions because its grammar is structured differently; but English is not Latin, and borrowing that constraint produces sentences nobody would naturally say. The alleged correction of "Who are you going with?" into "With whom are you going?" is grammatically possible but stylistically unnatural in most contexts. Winston Churchill is often (possibly apocryphally) credited with the retort: "This is the sort of arrant pedantry up with which I will not put."
Understanding this distinction — between descriptive and prescriptive grammar — is the deeper lesson here. Descriptive grammar describes how speakers actually use language; prescriptive grammar prescribes how some authority thinks they should. Neither is simply "correct." Formal writing contexts — academic papers, legal documents, professional correspondence — often call for avoiding terminal prepositions as a matter of register and audience expectation, not because stranding is grammatically wrong. Informal speech and writing rarely calls for the contortion.
The practical skill is calibration: know that preposition stranding is a natural feature of English syntax in questions ("What are you waiting *for*?") and relative clauses ("the policy he argued *against*"), and also know that certain audiences and contexts expect the traditional pied-piped form ("the policy *against* which he argued"). Choosing between them is a rhetorical decision, not a grammatical one. The goal is not to blindly obey the prescriptive rule or to reflexively reject it, but to deploy the form that serves your purpose and audience without creating constructions so awkward they distract from your meaning.