Lie vs. Lay

To lay is to place something; to lie is to recline (though there are other meanings). Lay is followed by an object, the thing being placed. For example: He lays the book down to eat. To lie is to recline, as in: She lies quietly on the chaise lounge. The best way to explain it is that lie in the sense of 'to recline' or 'be situated' is intransitive and cannot take a direct object. But lay meaning 'to place something' or 'put down' or 'arrange' is always transitive and requires a direct object. Because lie is intransitive, it has only an active voice, while lay can be active or passive because it is transitive. Part of the source of the confusion is the past tense of lie, which is lay: She lay on the chaise all day. The past participle of lie is lain, as in: She has lain there since yesterday, as a matter of fact. The past tense of lay is laid, as is the past participle.