It’s no “lie”: Many people get “lay” and “lie” wrong a lot. So let’s “lay” down the rules.

The best defense is just to memorize the tenses and figure out which word you want. But there are some shortcuts, and if you have a dirty mind, it’s easier:

• If you do it to someone or something, you lay it.

• If you or the object is just resting, you or it lie.

Lay is a transitive verb, meaning it needs an object. (Hence the dirty mind: It takes two.)

Lie is an intransitive verb, meaning it acts alone, without an object.

So to decide whether to use lay or lie, decide whether it takes two to discuss what’s happening, and use only present tense: If it’s a solo act, you want lie: “I lie down.” If it takes two to tango, you want lay: “I lay the book on the desk.” Now apply the proper tense:

Lay (present tense), laid (past), laying (present participle), laid (past participle).

Lie (present tense), lay (past), lying (present participle) lain (past participle).

Because lay is both the present tense of the transitive version and the past tense of the intransitive version, confusion sets in, so put your dirty mind to work again: If you do it to someone (or something) today, you lay it. If you did it to someone or something yesterday, you laid it. If you were so tired yesterday after you laid it, you probably went and lay on your bed.

If you feel like just “laying” your head in your hands, despairing of ever getting it right, you’re on the right track. No lie.

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Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years. Follow her on Twitter at @meperl.