Commas before 'and': To Use or Not to Use, That is the Question

The relationship between commas and 'and' seems to have a checkered history, at least when it comes to lists. However, I have noticed that many of my authors tend to put a comma before 'and' no matter what its function is in a sentence. There are really only two times that there should be a comma before 'and': 1) when 'and' separates two independent clauses and 2) before the 'and' in a list. Of course, you need to understand what an independent clause is to be able to properly place the comma in use 1. The trick I use is to ask whether the clause following the 'and' can stand alone as a complete sentence. If it cannot, then it is not an independent clause and the comma before 'and' is incorrect. This is non-negotiable. Only independent clauses can have a comma before the 'and'. As for use 2, many decades ago there would not have been a comma before the final 'and' in a list. As it was explained to me back in the dark ages, the commas in a list stood in place of what would be multiple 'ands', so that having a comma before the culminating 'and' signifying the end of the list was redundant. However, times changed and having a comma before the 'and' in a list seemed very useful to let the reader know when the list was really coming to an end, so it is now the norm.

Comma usage is still evolving, and I recommend that authors have a reference book or two for that, as well as for just basic grammatical rules. I recommend either The CSE [Council of Science Editors] Manual for Authors, Editors and Publishers or Turabian's A Manual for Writers. I find both useful.