(I found myself starting to go on about how sound change affects grammar, but you said *one* concept!)

You could continue, if you'd like. *g* I'm interested in this stuff (in no small part due to my current fandom obsession), but I don't know exactly where to start with the reading to learn about it.

Thanks for the info, BTW. Now I have at least one tidbit of knowledge to use should I ever need to have my favorite character (a linguist) show off his knowledge. ;)