Growing up, "lie" was only used when someone (never moi, of course) was telling a whooper. "Go lay down" was used whenever the adults wanted us rugrats out of their hair. Now that I am a mother in need of peace, "lay down!" springs to mind all too readily. Since the Great and Gruesome Massacre of English Grammar is not a legacy I want to pass on to the Sprout, I make an effort not to lapse into colloquial speech, which is also why you'll never hear me saying, "We was going to the store," another common gem in my ex-neck of the woods.
So, when I want to know if I should choose "lie" or "lay", I simply substitute the verb with the proper conjugation of "sit." If sit/sits/sitting works, I know I need lie/lies/lying; if the sentence needs "sat" then I know I need "lay." Note that there is no "satting" because there is NO "laying."
Not when you need the verb "to lie;" check out this entry on Merriam-Webster, first usage, if you need the definition.
This is obviously not the right way to proceed if using the verb "to lay" (lay, laying, laid). That verb needs an object (something being laid down); in that case, you can see if "set" or "setting" makes sense. Sat vs set can be confusing for some, and in that case, use "put/putting" instead.
- "Go _______ down." You wouldn't say "go sat down;" however, "go sit down" makes perfect sense. You need "lie": Go lie down.
- "I was ________ down when the phone rang." The "was" says that we need the participle form (-ing). Laying or lying? Well, one wouldn't say, "I was satting;" so "sitting" is the obvious choice, hence: I was lying down when the phone rang.
- "She _______ sleeping, looking so peaceful that I could not bear to wake her to share such sad news." A deliberately trickier example. Without the context at the end of the sentence, both the present "lie" and the past "lay" could work. The "could not," though, lets us know we need the past tense, "sat" rather than "sit," so: "She lay sleeping..."
How about the perfect form, the "have(has) lain/laid," when the present/past sit/sat can't help you?
Here's the easy rule: LAID does NOT belong with LIE, ever. Period.
If you know the definition of "to lie" and know what you are trying to get your sentence to say, you can safely ignore the little voice telling you to insert "laid." You only use laid when talking about putting something--an object--down (the whole "set" verses "sit/sat" thing from above).
- "Get off your arse.* You have _______ there for hours and you need to get to work on your projects!" Is anything being set down? No, it is referring to you, in a prone position. You need to get up because you've lain there for hours.
- "Where have I ______ my glasses?" No one speaks like this outside of books, at least no one of my acquaintance; most people prefer "put," but who knows, you might need to use it someday. Like in that book you are writing. So, "where have I sit my glasses?" or "where have I set(put) my glasses?" The second one. Giving us: Where have I laid my glasses?
Another reason I haven't gotten around to making this post before is because I'm afraid of leaving something out, but there you have the basics about how I deal with lie vs lay. I hope it helps! For more tips, here is Grammar Girl's take on it.
Quick reference table: