LAY: to put down; needs an object (transitive)
LIE: to recline; never takes an object (intransitive)
For example, when you feel tired at the end of the day, you may LIE down. But you can’t “lie” a book anywhere, and you can’t “lay” down (no object) at the end of the day. But you can LAY a book on the table, LAY a sweater on the bed, or LAY a child in her cradle.
A problem with LIE and LAY arises because the word LAY appears in both word forms. Here’s a handy graphic:
You can see how you might get confused if you don’t memorize at least one the forms or don’t remember how the words function (object or no object). Until you get better at it, sometimes you just have to stop and break it down:
*The past tense of LIE is LAY so:
ex: “The pig lay in the mud after yesterday’s rainstorm.”
*The past tense of LAY is LAID, so:
ex: “Last week, I laid the TPS report on your desk.”
*The past participle of LIE is LAIN, so:
ex: “The pig has lain in the mud for hours.”
*The past participle of LAY is LAID, so:
ex: “I have laid the TPS report on your desk.”
The difference between LAY and LIE is important. It ultimately has to do with whether or not your verb is transitive (takes an object) or intransitive (no object). If you can’t remember which is which, try to remember the root TRANS. It’s like “transport” or “transfer,” moving something (an object!).
Another way to remember is that LIE is Intransitive because both have the letter “I“.