Rasmusen Weblog

Suppose someone says, "Standard Evolution is good because it is a falsifiable theory and Intelligent Design is not. Standard Evolution would be falsified if we discovered human footprints from the Jurassic Age." That is wrong. The footprints falsify Evolution, but they falsify Intelligent Design just as much as Standard Evolution. Where the two theories differ is not in saying that Evolution occurs, but in saying how it occurs. Thus, a falsifiability test of Intelligent Design or Standard Evolution per se must rely on the particular theory's special features.

Each theory could be falsified, but only improbably. Standard Evolution could be falsified if evidence came up that God guided mutations-- say, the Second Coming, with miracles and a divine explanation. Intelligent Design could be falsified if evidence came up showing that all the improbable mutations are not improbable after all, but have a simple explanation we just haven't discovered yet, so there is nothing left to be designed. (Of course, a weak form of Intelligent Design, not falsifiable, is that God is guiding even the ordinary mutations that easily explained by natural causes.) Or, Intelligent Design could be falsified by showing that no guiding intelligence exists-- a negative that is very hard to prove.

Let's focus on a particular form of Intelligent Design: that the Biblical God, Jehovah, is the intelligent designer. The problem then is that to falsify Standard Evolution we need to show that God exists, and to falsify Intelligent Design we need to show that God does not exist. Both are tasks, which, even if the premise in each case is true, are of the same order of difficulty. If it is hard to falsify Intelligent Design, it is also hard to falsify Standard Evolution, which is "Not-Intelligent-Design".

Now let us move to the general case.

Consider the theory (akin to invoking God, as X), THEORY 1. "If X is true, then Y will happen."

but suppose we cannot tell if X is true or not (though we can tell if Y happens or not). Theory 1 is nonfalsifiable.

A second theory says, THEORY 2. "If Z is true, then Y will happen."

and we can tell if Z and Y are true or not. Theory 2, you may say, is falsifiable. If we find a case where Z is true but Y did not happen, we have falsified the theory.

Theory 2, however, can also be written as THEORY 3. "If Z is true, then Y will happen, even if X is false."

Theory 3 and Theory 2 are the same aren't they? Theory 3 just makes explicit a detail which is implicit in the statement of Theory 2.

But Theory 3 is not falsifiable. To falsify it would require us to find a case where Z is true, X is false, and Y happens. But we cannot tell if X is true or not.

Thus, I conclude that Theory 2 is not really falsifiable. Since for any theory I can come up with a competing theory which, like Theory 1, is nonfalsifiable, and that competing theory's falsity is implicit in the original theory's statement this means no theory is falsifiable. Comments are very much welcome. Is this idea well known? Is there a flaw in my reasoning? Even if true, does not it not matter to the usefulness of the idea of falsifiability?

I will add as a postcript that falsifiability is actually a very useful idea. It's just that its usefulness is not so much in deciding whether to accept a theory or not as to figure out if it is coherently stated. If I ask myself,"What would falsify this theory?", I am forced to think about what the theory actually means, and frequently I find I don't know what I'm talking about-- that I hadn't really stated a theory to begin with.