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lay, lie

lie (lying), lay, lain:
            Intransitive verb meaning to recline, takes no object:
                        The hat is lying on the floor
                        it lay there all day
                        it has lain there for a week now

lay (laying), laid, laid:
            Transitive verb, takes an object:
                        Lay the hat on the chair.
                        He laid it down quickly
                        he had laid it there before
                        it had been laid down quickly

Note: When lay is used in the passive voice, there is no object.

Idiomatic:     The hen is laying.

The nautical use of lay (lay at anchor and when meaning "to go," lay forward or aloft), though intransitive, is idiomatic.

To lay low, meaning "to bring down," should not be confused with to lie low, meaning to "stay in hiding."