Even people who think that they have perfect grammar mess this one up from time to time. Even though they may have similar meanings, there is a very distinct difference between lie and lay.
Starting with Present Tense
Let’s first differentiate between the meaning and usage of these two words.
Lie refers to the act of reclining (ignoring the other meaning of saying something that isn’t true). In other words, the subject is taking an action without the necessary involvement of an exterior object.
Dracula is going to lie down now, because he’s tired.
You should lie on your stomach and be quiet if you don’t want to get caught by the Boogeyman.
This is what is called a complete verb, because it doesn’t require an object. The shortest sentence could be two words: I lie.
Lay refers to the act of placing something, and that is the critical difference. The action is not being taken by the subject on him or herself. The action is being taken by the subject on some other object.
Jack lay the amulet on the monster’s chest.
Should I lay the carpet right here or over there?
The verb “to lay” will always require a direct object. It has to be done to something.
And Now It Gets Complicated
The present tense of “lie” is “lie.” I lie down right now, you lie down, and he lies down. However, the past tense is “lay.” I lay down yesterday, you lay down, and he lay down. And the past participle is “lain.” I had lain in bed for hours by the time the werewolf appeared that night. You had lain and he had lain.
The present tense of “lay” is “lay.” I lay down the book. The past tense and past participle are both “laid.” You laid the book down on the desk before leaving. He had laid the book on the desk.
It’s likely because of this crossover of terms that people get confused. The past tense of “lie” is “lay,” but the present tense of “lay” is also “lay.” And we don’t really hear or read the term “lain” all that often in casual speech, but we hear “laid” more often. When you combine the complications of definition with the complications of proper verb tense, you’re left with a very complex grammar situation.
Lying in Wait, Laying It on Thick
This can be hard to remember, so the only way you’ll get it is with practice. Write lots and read more. After a while, you’re more likely to get it right, because it’ll sound or feel right. Then, you can lie down and relax after you’ve laid out all your words on the page.