When should I use "which" vs "that"?

Question

For example, the sentence "All students must take an advanced legal writing class which includes legal drafting."

Answer 1

That is essential, and which is non-essential, or not as important, and typically gets a comma.

I would go with the following: All students must take an advanced legal writing class, which includes legal drafting.

The main point is the writing class. The legal drafting is additional, one of several courses, so a minor point.

Answer 2

There's a bit of ambiguity in this sentence. Does this refer to a legal-writing course containing a drafting component? Or does this mean that legal drafting qualifies as an advanced legal writing course? There are two possible edits:

A. All students must take an advanced legal writing class that includes legal drafting.

B. All students must take an advanced legal writing class, which includes legal drafting.

Answer 3

If your point is that the legal writing class includes legal drafting. I would think that you need to use "that," as in "All students must take a legal writing class that includes drafting."

If you want to describe the legal writing class, that is, give additional information about it, you would use "which includes legal drafting." However, I doubt that legal drafting would be the only component of the class. I would think that if you want to use which, you would need to list more components of the class, as in "All students must take a legal writng class, which includes A, B, and C."