I taught Rhetoric and was a Writing Center tutor at the University of Iowa for a couple years, and I was just reminded of a really great resource about comma usage that I used to recommend to students.

The Purdue OWL (Online Writing Center) has a short presentation that explains proper comma usage in a way that I think you'll find clear and accessible.

There is NO SHAME in needing a refresher session on punctuation rules!

Better to learn now than not at all!

Lucy

Book Country Community and Engagement Manager

Punctuation exists to make life easier for the reader.   Punctuation rules changed when more people became literate--when the person reading was not also reading aloud for others to hear.  Punctuation rules also change with fashion and with location: American English punctuation conventions are not the same as British English conventions.   And that includes comma use.  Winston Churchill, one of the great 20th c. English writers (in addition to the rest of his talents)  broke conventions when he felt his usage increased clarity.   (Some of you may have run across his retort to the person who "corrected" something he'd written with the note that one must not end a sentence with a preposition...Churchill wrote back "That is something up with which I will not put.")   Earlier writers--and Churchill--used commas where a speaker would pause, in addition to the places modern American rules agree they're correct. 

Why would these differ?   Because American rules are based not on natural speech, but on notions of structure held by 19th century academics who were trying to teach a lot of people quickly.  That the comma had been used as a breath mark for centuries didn't matter to them--it was hard to explain to an immigrant unfamiliar with English how to write understandable sentences by "feel"--they needed hard rules, it was thought.   (Linguists would probably disagree.) 

But what matters most to a writer is a reader's understanding of the writer's words.   If the writer's unusual use of punctuation does not confuse the reader--or if it enhances the reader's understanding--then it's justified.  If it confuses the reader, it's not. 

Thanks, Lucy.  I realize (reading my comment over a month later) that I was more forceful than necessary.