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Lay and lie are two of the most misused verbs in English. Or maybe not misused as much as they are confusing. They are irregular verbs, which means their conjugations don’t follow the same rules as regular verbs.
Their conjugations are confusing, perhaps, because both use lay as one of the verb forms. Confusing, also, because lie has a meaning other than the one pointed out here. (The regular verb to lie—meaning tell an untruth—follows the conjugation rules for regular verbs.)
When do you use lie and when do you use lay?
Lie means repose or recline.
Lie is intransitive—it doesn’t take an object. This means that someone or something lies, but that someone or something doesn’t lie something else.
Present tense: I lie down. (You could say, I lie on my bed. This is not taking a direct object. You are not saying, I lied my bed.) I need to be lying down. She lies down.
I want to lie down; lie down before you fall down
Past tense: Yesterday I lay down.
Future: Tomorrow I will lie down.
Perfect: I have lain down in that bed. I had lain down in the past. I will have lain down for 20 hours straight.
Lay means to put or place.
Lay is transitive—it requires an object. This means that someone or something puts or places something else somewhere.
Present tense: I lay the paper on the desk. I’m laying the paper on the desk. She lays the paper on the desk.
Past tense: Yesterday I laid the paper on the desk.
Future: Tomorrow I will lay the paper on the desk.
Perfect: I have laid the paper on the desk. I had laid the paper on the desk. I will have laid the paper on the desk.
A visual comparison may be helpful:
I lay (place) the paper. All long a sounds that remind you that lay means to place and requires an object (paper).
People lie and when they do, they are lying, not laying.
Laid is never used for lie. I laid down [or I had laid down] for a nap is wrong.