Usage and Grammar

Q. Lie down on your stomach or lay down on your stomach? M-W.com suggests “lie down” is preferable to “lay down.” Please clarify.

A. Merriam-Webster ought to know: “lie down on your stomach” is correct. “Laying down” requires an object: you can lay down your burdens, your money, or the law. You can even lay your body down, as long as body is included as the object. However, “lay down” has now become so popular for any and all constructions that it’s hard to call it incorrect, although major dictionaries and usage manuals do not yet accept it.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]