How to rigorously define independent clauses? [closed]

Question

Consider the following sentence:

The independent filmmaker Ira Sachs’s drama “Keep the Lights On,” which opened on Friday, is neither an especially good movie nor an especially bad one, but it is an exemplary one.

(source: http://www.newyorker.com/online/blogs/movies/2012/09/the-problem-with-the-liberal-cinema.html#ixzz25u38hVsZ ).

I am confused about the comma that precedes "but." Is "It is an exemplary one" an independent clause? The rule of a thumb I use is a can-it-stand-by-itself test; the sentence above sounds kind of awkward by itself, though I guess it could work. If it's not an independent clause, then why the comma?

Answer 1

It is an exemplary one is an independent clause because it is not subordinate to another clause. That would not be the case if, for example, it was even if it is an exemplary one. It is not the comma that determines whether a clause is independent or not. The comma, like all punctuation, is a convention used to help the reader. In this case, it is used to show that two clauses, which could in principle be separate, have been joined together.

Answer 2

Any clauses that are conjoined with and -- or disjoined with or -- are independent clauses.

But means the same as and, but includes extra information about expectations.

1. Bill washed the dishes and Mary dried the dishes.
2. Bill washed the dishes or Mary washed the dishes.
3. Bill washed the dishes but Mary dried the dishes.

These are all compound sentences with two independent clauses each. In writing, commas are optional before the conjunctions; -- as always, commas should be written only if they are pronounced, and not otherwise.