The basic rule
Lay is a transitive verb — it needs a direct object, something being placed: "Lay the book on the table." Lie is intransitive — no object, describing the subject reclining or resting: "I want to lie down for a while."
The trick
Ask: is something being placed/put down BY the subject onto something else? If yes, use "lay" ("lay the baby down"). If the subject itself is reclining, use "lie" ("I lie down").
Why it's so confusing: the conjugations
| Verb | Present | Past | Past participle |
|---|---|---|---|
| Lay (put down) | lay | laid | laid |
| Lie (recline) | lie | lay | lain |
Notice that the past tense of "lie" is "lay" — which is exactly the present tense of the other verb. That overlap is the main source of confusion.
Examples
Lay: "She laid the papers on the desk." "Lay it down gently."
Lie: "He lies on the couch every afternoon." "Yesterday, I lay in bed all day" (past tense of "lie").
Frequently asked questions
What's the simplest way to tell lay from lie?
"Lay" needs an object (you lay something). "Lie" doesn't (you yourself lie down).
Why is "lay" the past tense of "lie"?
It's a historical quirk of English — the past tense of "lie" (recline) happens to be "lay," the same spelling as the present tense of the other verb "lay" (put down).
"I'm going to lay down" — is that correct?
Strictly, no — the correct form is "I'm going to lie down," since no object is involved.
What's the past participle of "lie"?
"Lain," as in "I have lain here for an hour" — though in casual speech this form is often replaced informally.