Lay and Lie are among the most commonly confused verbs in English—at least when it comes to their shared meaning of “put or rest in a place.” Both words also have other meanings, which I’ll cover below.
Lay is a transitive verb, and lie is an intransitive verb (transitive verbs have an object; intransitive verbs do not have objects)—but here’s what causes much of the confusion: lay is also the past tense of lie:
Anna lies in bed all day. (intransitive, present tense)
Anna lay in bed all of yesterday. (intransitive, past tense)
Please lay the book on the table. (transitive, present tense)
Anna laid the book on the table. (transitive, past tense)
So, it is incorrect to say “She lied in bed all day”—unless it means “She was telling people things that are not true, and did so while she was in bed all day.” This is because lied is not the past tense of lie as in “lie in bed,” but it is the past tense of lie as in “saying things that are not true.”
Lie, with the meaning of “rest in a place,” can be used very generally:
Our house lies on the edge of town.
The responsibility lies with the parents.
The meaning of poetry lies between the lines.
Lay also has a wide variety of uses related to the meaning “to put something down on something”:
The fighter laid into his opponent with punches and kicks.
The workmen laid down bricks for a new patio.
Does your chicken lay eggs?
Rita laid blame for the accident on her mistakes.
They laid a trap for the monster.
Both words can also be nouns, but with completely different meanings.
A lie is “an untruth”:
Do not believe his lies!
While a lay is “the shape of the land”:
You could see the lay of the whole valley from Peter’s front door.
Finally, there is another meaning of the noun lay, meaning “ballad”—a traditional type of song or poem, from the European Romantic tradition, which tells a story, such as The Lay of Beren and Luthien, a long poem by J.R.R. Tolkien (which will probably be a movie someday).
And of course no discussion of lay would be completed without mentioning the famous song, Lay Lady Lay. The song probably adds to the confusion, but never pass on the chance to share a Bob Dylan song!