What Is Proper Grammar?

Theoretically, proper grammar are the set of rules that are universally true for a language.

In actuality, a universal "proper" grammar doesn't exist. (I'm speaking for English, here. I don't know enough Spanish to know about that language.) Even within the United States, rules vary according to source.

Now, English does have certain little rules that are universal, or at least rules that I haven't heard any source contradict yet. Like those two commas in the previous sentence—those are correct according to every source I've read (which would be several). Those rules are therefore "proper" grammar, though often with exception clauses. For example, someone might omit the comma after "Now" to emphasize how he wants it to be read.

Otherwise, "proper" grammar is whatever grammar is considered correct by your source. Should a list of three or more items have that [serial] comma before the and? Some sources say "Yes," and some say "No."

These differences do not mean that there is no such thing as "proper" grammar. There is. The distinction is that different sources define proper grammar in different ways.

Therefore, proper grammar would be the grammar rules considered correct by a particular grammatical source.

P.S. If this sounds a bit disjointed, please forgive me. My brain started shutting down for the night over two hours ago.