A preposition shows how a noun or pronoun relates to another word in the sentence. The noun or pronoun after it is its object. Together they make a prepositional phrase: in the box, after lunch, with Sam. This builds on Kinds of Nouns.
Common prepositions: about, above, across, after, against, along, around, at, before, behind, below, beside, between, by, down, during, for, from, in, into, near, of, off, on, over, past, through, to, toward, under, until, up, with, without.
Key idea
A preposition always has an object. Ask “preposition what?” or “preposition whom?”: under what? the blanket.
Why it works
Prepositions carry the relations between things: place (under, beside), time (after, during), direction (to, toward) and more. Finding the object also keeps you from a common trap: the subject of a sentence is never inside a prepositional phrase.
Worked example: Preposition or adverb?
Is up a preposition in “She climbed up the ladder” and in “She looked up”?
- “Up what?” In the first, the ladder: it has an object, so up is a preposition.
- In the second, nothing follows: up tells where she looked. It is an adverb.
Answer: preposition, then adverb
Common mistake
Calling words like up, down, in, out and around prepositions every time. With no object after them (“Please sit down”), they are adverbs.