Sit describes a person, animal, or thing resting in place, as in she sat quietly in the corner, while set means to put something down in a particular position, as in he set his keys on the table. A simple memory hook: you sit yourself down, but you set something else down — set almost always needs an object to act on.
The core difference
Sit is what a person or thing does by resting somewhere; set is what you do to something when you put it down.
- sit — to rest in an upright position, or to be located somewhere: The old house sits at the top of the hill.
- set — to put something in a particular place or position: She set the vase on the windowsill.
How to tell them apart
The clearest test is whether there's an object being acted on. "She sat on the chair" describes what she herself did; "she set the vase on the shelf" describes what she did to the vase. If you can ask "set what?" and get a sensible answer, set is the right word; if the subject is the one doing the resting, sit fits.
The two verbs share a history — set comes from Old English settan, literally "to make sit," so set has always meant causing something else to be in a resting position, while sit describes that resting position itself. The mix-up shows up constantly in everyday writing, especially with objects like vases, cups, and books that get "sat" on a table when they were, technically, set there.
