Lay and lie are frequently confused verbs that have similar meanings (to do with objects or people lying horizontal on a surface), but for this one big detail - lay is transitive and always has a direct object; lie is intransitive and will never have a direct object.
The reason it seems confusing is that the past tense of lie also happens to be called lay. But this lay should be compared to laid - the past tense of lay. A great way to remember is to chant the present, past and past participle of each verb as one unit: lay-laid-laid and lie-lay-lain.
Lay means to set something down, to place, or to arrange it over or onto a surface. It is typically used in reference to inanimate objects — for example, I am going to lay out these candles on this shelf, or please lay this book on the table. The verb lay will always have a direct object.
Lie is a verb that means to recline, or to rest in a hosizontal position. It is often used to refer to people or animals — for example, I need to lie down in bed, or the dog lies in front of his master's grave for hours.
In this video, Emma explains the difference between lie and lay:
Presence of Direct Object
Lay is a transitive verb, and will always, without exception have a direct object. In other words, this will involve two nouns:
- the subject (i.e. the person who lays something down),
- an object (i.e. the something which the person is laying down).
- E.g. Jack lay the book on the table.
(Always ask: Jack lay WHAT on the table? - And there should be an answer: The book.)
- I lay my head in her lap.
(WHAT did I lay in her lap? - My head.)
The adverb phrase - i.e. the phrase indicating where the action took place need not necessarily have a noun.
The words 'table' and 'lap' in the above examples allude to where the action took place, but we really don't require any nouns here. E.g. I lay the book there. I lay my head down.
Lie is an intransitive verb, and is only about what the subject is doing (by and to himself). It will never have a direct object, and the only required noun is the subject.
- E.g. Jack lies down (on the bed).
(Ask: Jack lies WHAT? And there's no answer, because there's no direct object.)
- I lie on the grass.
(I lie WHAT? No answer.)
Again, the adverb phrase may or may not have a noun. Do notice that when you ask Jack lies WHAT?, "on the grass" answers "where," not "what."). And even here, the adverbial noun need not exist. E.g. Jack lies down. I lie there.
Action vs Position
Lay will always denote an action in progress; a motion. When you say Jack lays the book on the table, the book moves with Jack's hand on to the table. My head moves down onto her lap.
Lie always denotes and unchanged position. When you say Jack lies on the bed, you refer to Jack's position, i.e. he is already there, lying on the bed.
Why the Confusion?
Because unfortunately, the past tense of lie happens to be lay. This is how the two verbs look in the present, past and past participle forms:
Jack lays the book on the table. Jill lies on the bed.
Jack laid the book on the table. Jill lay on the bed.
Jack had laid the book on the table. Jill had lain on the bed.
How to Remember
This confusion can be allayed by two simple tricks:
1. Chant the tenses in your mind as though you're still in elementary school: lay-laid-laid lie-lay-lain
2. Always ask "WHAT?" after the verb and look for a direct object, regardless of tense.
Present Tense: Jack lay the book on the table. Jill lies on the bed. (Jack lay WHAT? - The book. Jill lies WHAT? - No object.)
Past Tense: Jack laid the book on the table. Jill lay on the bed. (Jack lay WHAT? - The book. Jill lay WHAT? - No object.)
Jack had laid the book on the table. Jill had lain on the bed. (Jack had laid WHAT? - The book. Jill had lain WHAT? - No object.)