This has been driving me nuts for a while now. But when reading various articles, and it's not the same for every one, writers are adding a second comma in their sentences. I remember learning in English class that when writing a sentence that includes three subjects, it's structured as follows - subject, subject and subject. So when did it become acceptable to structure the sentence - subject, subject, and subject. That just feels wrong even typing it for this example.

So, I went online to try to find the reasoning. Yeah, I didn't get an answer. In fact, I got that both are correct.

What?!

And there is not a specific instance when it's proper to structure the sentence in such a manner.

What?!

Is this common core for English?

According to grammarly.com, this is called an Oxford comma. I have never heard of this sorcery. I screen shotted this exert from their website explaining what it is and how to use it.

grammarly.com

So it's ok just to write all willy nilly as long as you do it the same throughout the same article?

It drives me nuts and I will never do it - subject, subject, and subject. That is just plain incorrect to me. If you are an English teacher or some kind of professional writer, maybe you can explain this to me better because, frankly, this is just dumb.