Historical linguistics is a field that many people don’t know a whole lot about. We all speak a language, and we all know that our words came from somewhere else, but we don’t always have the clearest idea as to where or why. So people speculate and come up with plausible explanations of word origins—what we call folk etymologies.
The problem is that etymologies are quite often not intuitive, nor can they be determined solely through deductive reasoning. Words take very circuitous paths on their way from history to the present. Over the course of a couple thousand years, a word can change so thoroughly that it becomes unrecognizable. Words that look similar aren’t always related, and words that are related don’t always look similar.
Take, for instance, just a few of the Indo-European words for five: fünf (German), cinq (French), pump (Welsh), cóig (Scottish), pénte (classical Greek), pyat’ (Russian), pãch (Hindi), and panj (Farsi). Believe it or not, all these words—as disparate as they seem—are related; they come from the same word, *penkwe. They may look very different, but they all changed via systematic sound changes.
Think of it like a Rubik’s cube: you start out with all the colors on their respective sides, and then you start turning the faces. Pretty soon, it’s a complete jumble. There doesn’t seem to be any sort of pattern to the arrangement of the colors now, but they didn’t get that way by chance; you made a specific series of twists to get them to end up the where they are.
This means that you can’t assume two words are related just because they look alike, or that two words aren’t related because they don’t look alike. Looking alike is a good start, but that’s all it is; next you have to find the systematic changes that connect the words. Historical linguistics isn’t just guesswork or finding lists of words that have a couple of sounds in common. It’s about knowing where the language has been and how languages change and then filling in the blanks.
There are lots of books and sites out there that purport to show that German comes from Hebrew or that Welsh and Hindi are closely related or any number of other weird claims. However, the thing that these all lack is systematicity. Without a system and without a knowledge of how languages change, historical linguistics is nothing more than a meaningless matching game. You can take the stickers off the Rubik’s cube and rearrange them to look good, but you haven’t really solved the puzzle.