When to use "I" and when to use "me"

Question

Pat from Australia asked: Which of the sentences below is correct and why?
 

• Jill took Justin and I to the shop.
• Jill took Justin and me to the shop.

Answer

This is a part of a bigger question that troubles both learners and native speakers of English:  when to use I and when to use me. 

The difference between I and me

Both I and me are 1st person singular pronouns, which means that they are used by one person to refer to himself or herself. I is the subject pronoun, used for the one "doing" the verb, as in these examples:

• I am studying for a Russian test. (I is the subject of am studying.)
• I can speak Russian, but I can't read it very well. (I is the subject of can speak and can’t read.)

Me is the object pronoun, used as the object (or receiver) of the action of the verb, as in these examples:

• My math teacher encouraged me to come for extra help after school. (Me is the object of encouraged.)
• She asked me to bring my homework. (Me is the object of asked.)

 
The confusing part

What gets confusing for many people is which form to use when there are two subjects or objects linked with and, as in these examples:

a. Jenny and me/I (?) joined the chess club.

b. Jill took Justin and me/I (?) to the shop.

In sentence a), Jenny and me/I are the subjects of the verb joined. Therefore, the subject pronoun, I, is considered correct. You will certainly hear native speakers say, “Jenny and me,” and it may be acceptable in spoken English, but most traditional grammarians and English teachers will disapprove. Don’t use it in writing.

The opposite is true for sentence b), which is the original example from above. Justin and me/I are the objects of took. Therefore me is considered correct by most grammarians and teachers, although you will hear people say, “Justin and I.” Again, don't use it in writing.

Hint
If you’re having trouble deciding which one to use in a particular sentence, here's a hint: Take out the other person, and it should be clearer. You are not likely to be tempted to say, “Me joined the chess club,” or “Jill took I to the shop.”

I hope this helps.