Here's why:
* Lay is the past tense of the verb "to lie" when it means "to place something down."
* Lain is the past participle of the verb "to lie" when it means "to be in a reclining position."
Correct phrase: The book lay on the table.
Here's why:
* Lay is the past tense of the verb "to lie" when it means "to place something down."
* Lain is the past participle of the verb "to lie" when it means "to be in a reclining position."
Correct phrase: The book lay on the table.