Learn the Difference Between "Lie" and "Lay"The main difference between the two words is that lay is a transitive verb, while lie is an intransitive verb.
The important part of that page - though I urge you to read the whole thing so that I stop feeling like my eyeballs are going to explode when I talk to people - is this:
So here's the drill:
~You need to lie down today, yesterday you lay down, in the past you have lain down.
~Today, you lay the book on the table. Yesterday, you
laid the book on the table. In the past, you have laid the book on the table.
Jolly good, hope that clears everything up. I mention this largely because the epically pointless lecture I just gave in the margins of a Word document failed to use the words "transitive" and "intransitive" because I'd forgotten them, along with an awful lot of other things like "why the fuck I am bothering with being awake". But it mostly involved "lay is something you DO to something, LIE is something you do yourself" which seems reasonably close to the actual grammatical explanation.
Do not ask me why I have taken a demented set against this, considering the magnitude of titfucking grammar mistakes I make all the time, it's just been gnawing away at me for about EIGHTEEN MONTHS NOW and it makes me want to commit murders, especially when I go on well-regarded news sites and find myself staring at the word "layed" which DOESN'T EVEN EXIST. I can understand the confusion ("played", as opposed to "plaid", which is something else entirely) but at the same time NEWSPAPERS YOU HAVE COPY EDITORS RIGHT.
Petty annoyance is petty. Don't care. Whining anyway.