What's a coordinating conjunction?

It's a word (called a conjunction -- words like and, but, or, nor, yet, so) that links words or word groups that have the same function.

Dogs and cats fight.

My nose, but not my feet, smell.

I've got to pass this course, or I'll have to take it in summer school!

Neither the man who came to dinner, nor the woman who accompanied him brought a gift.

The dress was expensive yet ugly.

He came early so he could taste the shrimp.

Challenge: some of these sentences contain commas and some don't -- can you explain why?

Dogs and cats fight.
(The subject is a compund noun phrase -- no comma necessary)

My nose, but not my feet, smells.
(Contrasting element)

I've got to pass this course, or I'll have to take it in summer school!
(Two sentences are combined. Beware: If you omit the conjunction, you've written a comma splice.)

Neither the man who came to dinner, nor the woman who accompanied him brought a gift.
(ditto above)

The dress was expensive yet ugly.
(2 adjectives joined by a conjunction; no comma necessary.)

He came early, so he could taste the shrimp.
(Two sentences are combined. If you omit the conjunction, you've written a comma splice.)

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