Some time back, I was working on a report with a coworker. One of the sites that we had to discuss in the report was located on an athletic field. The site was a simple flake scatter, a site consisting of the pieces of obsidian left over after a flaked stone artifact is manufactured. Unsurprisingly, the flakes were almost all broken.
Now, there are two ways that one tends to get a broken flake: 1) it is broken when the tool is being manufactured, and often such broken flakes indicate either a flaw in the material, or an error made by the person making the tool; 2) the flakes are broken after it is created, usually by being trampled or having some heavy object fall on it. A well-trained lithic analyst may be able to tell these types of borken flakes apart...but most of us working int he field cannot.
However, this seemed pretty simple - a site with an abnormally large number of broken flakes is located on an athletic field. One thing that will happen for certain is that the flakes will be trampled, which means that the most likely cause of the broken flakes is tramapling.
My coworker was not pleased with my conclusion. He entered my office with the site record, and said "you can't say that the broken flakes were caused by the athletic field!"
I looked up and said "uh, yeah, I can."
He got an annoyed look on his face and responded "there's alot of ways that a flake can be broken."
"Yes. Yes there is. One of those ways is being stepped on by a soccer player. Alot of soccer players will break alot of flakes."
He thought for a moment, and said "I have an alternative hypothesis. You could end up with all of these broken flakes is you have one person who is really bad at flaking stone."
This was, of course, technically true. But there's some deep flaws in the hypothesis, which I proceeded to point out.
"Okay, so let's say that you have this one lousy flintknapper*, like you suggest. Why would he be making tools only in this area, which he'd have to have been to account for all of the broken flakes."
He gave this a moment's thought, and replied "well, maybe they put all of the bad, or learning, flintknappers in this one spot."
"Right, okay," I responded, "here's the thing with that - knapping obsidian produces alot of sharp edges, obsidian is glass, after all, so it's in your best interest to limit the number of places where little pieces of it are just lying around. So, assuming that you had a number of learning flintknappers who keep producing broken flakes, why would you segregate them to spread out the area where the broken glass is lying around?"
To which he said "Well, obsidian flakes are in alot of sites, they're not usually alone"
"True, and a fair point." I responded "there are sites with clear obsidian flaking task areas, but often it's not in a designated area. Still, you're assuming that the people of this area segregated bad and/or learning flintknappers. We have no evidence of that: no ethnographic records, no archaeological sites showing only poorly formed tools and broken flakes, nothing to give us the 'bad knappers' that your hypothesis requires. You are having to make some odd assumptions for your hypothesis to make sense."
"Well," he looked at me smugly, "you're making alot of assumptions, too."
"No, I'm not. We know that the people in the area flaked obsidian. We know that obsidian flakes often break if trampled upon. We know that alot of running feet on an athletic field would trample on flakes. Those are all knowns, not assumptions. All the record does is conclude that a bunch of broken flakes found on an active ethletic field probably indicates that the flakes were broken by trampling, which makes no real assumptions and just connects a few observations with known facts."
He shook his head and walked away. I got the record, and the report to which it was appended, to say what I wanted. But for the life of me, I have never been able to figure out why this guy was so sold on a bizarre notion, and why he wanted to argue with me about it.
*Flintknapping is the generic term used for making stone tools