Lie vs. lay

This page is part of the Frequent Grammar Mistakes category.

Background
The word lie is an intransitive verb, and the word lay is a transitive verb. Many people confuse the words lie and lay, especially considering that some of their verb tenses are similar:

When to use lie
Lie is an intransitive verb, which means it doesn't need an object to make sense. Let's look at some examples: I need to lie down. Remember that objects tell us the WHO or WHAT after the verb. We have a where, but no what, so this verb is intransitive. But what if I need the past tense? I had such a headache, I needed to lay down. This is where many people get confused, because the past tense of lie is lay. I had lain down because of my headache. If we need the past participle, then lie becomes lain. Remember, we need the participle because we used the auxiliary/helping verb had.

When to use lay
The word lay is a transitive verb. It must have an object. Consider these examples: I need to lay the heavy book on the table. Objects answer who/what. Ask yourself, "Who/what do I need to lay on the table?" The book was so heavy, I laid it down. The past tense and past participle of lay are the same. And again, we can answer the question ("Laid what?" "It").