Language is always changing. Just talk to a teenager who uses a lot of slang, and see if you understand them.
Written language fossilizes it and makes it stop changing. The Bible, especially the King James Version, has been very influential on keeping language the same because it has been so widely read. The KJV is still quoted frequently in some circles, and some of its phraseology is very much a part of commonly spoken English.
For example, I had long thought that the word “stuff” was of fairly modern origin, scorned as it was by my English teachers. But then I discovered that “stuff” is in the KJV. Some common clichés that came from the Bible are: “a wolf in sheep’s clothing,” “a broken heart,” “as white as snow,” “bite the dust,” and many more. You can find more of them here.
Without a written language, there is no “right” or “wrong” way to speak. In small communities with no written languages, grandchildren and grandparents have difficulty communicating with each other, the language has changed so much.
Actually, that sometimes happens here, too. (See earlier comment about slang.)
Language change is quite simple. For example, take the word “apron.” I might say, “I need to find an apron.” Well, the word used to actually be “napron,” and people would have said, “I need to find a napron.”
Say those out loud and see how similar they are, and how easy it would be to change from one to another, especially if there was no written language or if literacy were very uncommon. (This, by the way, is just one method of language change, and is called rebracketing.)
Kids do this kind of thing all the time – misunderstanding a word like that. Heck, even adults do it. My husband and I were talking the other day and he mentioned Oahu. I asked, “What’s a wahoo?” “You know” he said, “the island?”
“In Hawaii. O-a-h-u” (spelling it out). And so, thanks to written language, my misunderstanding was cleared up.
My favorite example of modern language change is “a whole nother.” What on earth is a “nother”?
You might want to say something like, “We need another pizza,” but you want to add emphasis, because it’s really important that you get another pizza, so you add the word “whole.”
But where in the sentence should it go? “Whole another pizza” obviously doesn’t work, and no native English speaker would say something like “another pizza whole.”
“Another whole pizza” is technically correct, but sounds awkward. So “whole” gets inserted into “another,” giving us “a whole nother pizza.”
You may not even realize you are using it, since it has become part of everyday English.
Grammar nazis frequently mourn the bastardization of our beloved language, but it’s already bastardized. English is already a mishmash of words, grammar, and figures of speech borrowed from many languages.
Language is dynamic and ever changing.
I am a bit of a grammar nazi, and can become very agitated when people do things like use “literally” incorrectly or don’t use adverbs properly. But I let things like “whole nother” slide since, after all, language is always changing, and, anyway, I use it myself!
Most of my information comes from Our Magnificent Bastard Tongue and Tower of Babel, both my John McWhorter. If you’re interested in learning more, I highly recommend you read his books. They’re fascinating and Bastard Tongue is a fairly quick read.