This thread reminds me of my grammer teacher.

What about leaving off the second on instead?... I'd have to disagree and say that the two on's are necessary. For example, using two had's is perfectly valid:I think this is by far the most sensible approach. There are hundreds of different ways of saying the same thing.

@sayan_acharjee: I think you meant grammar...

Good written English (US)
Difference between?

and

Both forms are acceptable. The second form is more popular in the US. I used it for a while but found no advantages to justify the extra comma so reverted to the first form.

It's called the Oxford comma. They're much more common in the US than in the UK. There's an argument they're useful for listing things which are pairs of words (e.g. fish and chips, black and white etc.):Without the Oxford comma, that looks a bit odd ("black and white and other things"), whereas with the Oxford comma, it separates the items:

I didn't know that the "Oxford comma" is optional, I thought it's required.

Depends where you're from. The UK has them as an option; I believe in the US they're standard.

I didn't even know there was a term for that...I've always used a comma before the "and" in a list of items.

E.g. "One, two, and three." as opposed to "One, two and three.".

I also never knew it had a name until now.

That looks like you're specifying 3 options: A, B, and C + D.

And 4 options: A, B, C, and D.

To me, the last item in a list is always preceded by an "and", irrespective of whether there's a comma before that and or not. So, in that example, the list has four items. If it were written as:that would have three items ("A", "B", "C and D").

How about:
Chaplin, Keaton, Laurel and Hardy
or:
Chaplin, Keaton, Laurel, and Hardy

?

Well, if there were three groups, then it'd be Chaplin, Keaton, and Laurel and Hardy with the Oxford comma, otherwise it'd be Chaplin, Keaton and Laurel and Hardy without. However, in this instance, reordering the list is sometimes more sensible: Laurel and Hardy, Chaplin and Keaton.

If there were four groups, then the last example you've given makes sense as a list with the Oxford comma; drop the last comma and it's still valid as a list of four items. At least in UK English.

This is the thing about commas in particular, they're quite subjective. As far as I'm aware, there are no hard and fast rules about exactly where they belong. If you're into this sort of thing, Lynn Truss' book "Eats, Shoots and Leaves" (itself a phase whose meaning changes if you omit the comma) is quite entertaining. However, this subject is covered by many authors. A fairly definitive guide is the book "The Elements of Style", though it's more American English than English English.

Anyway, we don't usually bother with proper English in Oldham.
I've heard of that, but not read it. Something else for my Todo list.

Worth reading, it explained a lot of stuff that was never raised in school. And the book is somewhat entertaining too.