Well here's when you gotta bring out the big ol' Grammar Book back to refer to, because there IS a difference, not just in spelling but also pronunciation. It's also important to note the overlaps of these words in certain tenses, which makes it even more confusing.
First, it's important to know that lay is a Transitive Verb (TransV) while lie is an Intransitive Verb (IntransV). This means that lay requires a Direct Object (DO = something the action is done to) while lie (except for the meaning of 'telling untruths', for which a DO is optional) does not.
Verb Infinitive Past Tense Past Participle
lie lie lay lain
lay lay laid laid
Here are some altered examples of sentences using these, from Grammar Girl.
Blue = Lie, Pink = Lay, Yellow = Direct Object.
The present tense of lie and lay are rather easy to distinguish:
You lay down the sheets of paper.
You lie on the floor.
The past tense of lie is lay, so
Last week, Steve lay down on the floor.
The cat lay in the mud after it rained yesterday.
The past tense of lay is laid, so
Last week, I laid the TPS report on your desk.
Mary forcefully laid her ring on the table.
The past participle of lie is lain, so
Steve has lain on the floor for days.
The cat has lain in the mud for hours.
The past participle of lay is laid, so
I have laid the TPS report on your desk.
Mary has forcefully laid her ring on the table.
This is just a simple account of the issue. For more information, please refer to these sites (aka my sources):
Cheers and have fun with grammar. ;P
