Grammar Tips

Some grammar tips adapted from an english resource website.
Lain vs Laid
The English verb "lie" is complex and often problematic. Proper usage of its past tense forms like "lain" and "laid" are often confusing and used improperly. However, keeping some simple rules in mind makes it easier to use words like "lain" and "laid" in their proper grammatical context.Whether one uses "lain" or "laid" depends on the action being performed by the verb. "Laid" is the past tense of "lay," and "lain" is the past participle of "lie." The most simple way of understanding which form to use is by using it in context. For example, if one is resting or becoming prone, "lain" would be proper, as in "he has lain there for days." However, if one is placing something somewhere, "laid" is proper, as in "she laid the notebook on the desk."
   But lie and lay seem to give people more difficulty than do all the other irregular verbs combined. Here's why: The past tense form of lie is lay, so it's indistinguishable from lay in the present tense except in usage. (Sit and set, probably the irregular verbs that give people the most trouble next to lie and lay, for example, have no parts in common. It's sit, sat and sat but set, set, set.)

 The principal parts (most-common verb forms) of lie are:

lie (present,) lay (past) and lain (past participle).

     The principal parts of lay are:

lay (present), laid (past) and laid (past participle).

     As an aid in choosing the correct verb forms, remember that lie means to recline, whereas lay means to place something, to put something on something.
Lie
Present tense: I lie down on my bed to rest my weary bones.
Past tense: Yesterday, I lay there thinking about what I had to do during the day.
Past participle: But I remembered that I had lain there all morning one day last week.
Lay
Present tense: As I walk past, I lay the tools on the workbench.
Past tense: As I walked past, I laid the tools on the workbench. And: I laid an egg in class when I tried to tell that joke.
Past participle: . . . I had laid the tools on the workbench.