Lay vs. Lie

She laid the books on the table.

Lay is a regular verb. Its forms are:

Infinitive: to lay
Present Participle: laying
Past: laid
Past participle: laid
Present singular: lays

Lie

Lie means be down or be placed flat on a surface. It is an irregular verb. Its forms are:

Infinitive: to lie
Present Participle: lying
Past: lay
Past participle: lain (formal)
Present singular: lies

She was lying on the sofa.

A book lay open on the table.

Don’t lie in the bed all day.

There is also a regular verb lie. It means say something that is not true. Its forms are:

Infinitive: to lie
Present Participle: lying
Past: lied
Past Participle: lied
Present singular: lies

He lied about his age in order to get into the army.