Lay and lie.

Even native speakers of English have trouble distinguishing between certain verb pairs which share forms and meanings, the most commonly misused probably being lie and lay.

A transitive verb takes an object. Lay is a transitive verb: I lay the offensive soufflé before the embittered in-laws. The verb lay acts directly upon a person or thing, in this case the soufflé, which is the object of the verb.

By contrast, the verb lie is intransitive. It takes no object and indicates the state of its subject: The soufflé lies before the embittered in-laws. The soufflé is the subject and the verb lie gives its state. English has several pairs of verbs that act this way, one transitive and the other intransitive. It is easier to recognize the differences between them by considering the present, past, and past participle forms of each.

Lie/lay

present past past participle

lay laid laid

lie lay lain

Transitive: Today I lay the soufflé before the embittered in-laws. Yesterday I laid it before the embittered in-laws. I have laid it before the embittered in-laws.

Intransitive: Today the soufflé lies on the table. Yesterday it lay on the table. It has lain on the table since September when it was still marginally edible.

The lie/lay pair is particularly confusing as the past tense of the verb lie (lay) is the same as the present tense of the verb lay.

Other oft-mangled pairs:

Fell/fall

present past past participle

fell felled felled

fall fell fallen

He fells a tree and the tree falls. Yesterday he felled the tree and the tree fell. The fallen tree was felled by a felonious furry fellow who fells firs that fall fast.

Raise/rise

present past past participle

raise raised raised

rise rose risen

Raise the flag so they can see it rise above the landfill. When it rose, they could not understand why it would be raised where none had ever risen before.

She is raising a rose to rise higher than any other rose raised here has risen.

She rose late again today and then raised the issue of installing a luminous sundial for use before the sun has risen.

Hang/hang

present past past participle

hang hanged hanged

hang hung hung

The verb hang is a special case in that the older transitive verb hang/hanged/hanged fell into disuse and survived only through being used as a legal term for execution by hanging, while hang/hung/hung has come to be used in all other senses, both transitive and intransitive. (The equivalent verbs in German are still used in their full transitive and intransitive forms: hängen, hängte, gehängt and hangen hing gehangen.)

Transitive: They wanted to hang him today for rustling, but that was pointless as they already hanged him yesterday. They have hanged several rustlers, confiscated their potato chips, and threatened to hang one passerby who produced excessive noise with an eel skillet and a runcible spoon.

Intransitive: Today the revolting image hangs on the wall. Yesterday it hung on the wall. It has hung on the wall, evoking revulsion, for years.

Note that, in each of these pairs, the transitive verb is regular, taking ed for its past and participial forms (except for laid, which has mutated a bit from layed), while the intransitive verb is irregular.