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The verbs “lie” and “lay” are perhaps the two most confusing irregular English verbs. “Lie” has two meanings: It can mean “not to tell the truth”, or it can mean “to be in a horizontal position” (or, more generally, “to be located somewhere”). “Lay” means “to put something in a particular position” — that is, after you lay something somewhere, it lies there.
So far, so good, but when we start using these verbs in the past tense, things get confusing. “Lie” in the sense of not telling the truth (and in this sense only) is regular:
lie (not tell the truth) – lied – has liedIn all other senses, “lie” follows the pattern “lie, lay, lain”:
lie (be in a horizontal position, be located) – lay – has lainAs you can see, “lay” has two meanings. “I lay” can mean either “I was in a horizontal position” or “I put something in a particular position”. Which meaning is intended is always clear from the context because “lie” is never used with an object and “lay” is never used without one (we never “lie something”, but we always “lay something”). The distinction is also clear in the third person singular: “he lays” is the present tense of “lay”, “he lay” is the past tense of “lie”.
There are two more verbs which follow the pattern lie – lay – lain:
underlie (“be the cause of”, “lie under”) – underlay – underlain
overlie (“lie on top of”) – overlay – overlain
The verb “lay” also sometimes causes trouble. The archaic form of its past tense and past participle is “layed”, but this form is no longer used. The correct form in modern English is:
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