Frequent commenter Popperian often employs the “Possible Possum Gambit.” Here’s how he does it:
Barry: An effect cannot be brought about by a cause that is incapable of producing the effect. A pile of bricks can “cause” some things if they are organized in a particular way, a house for instance. But a pile of bricks is incapable of causing a mental image of an imaginary unicorn. Why? It should be obvious, but I will spell it out. A pile of bricks is in a different ontological category from a mental image of an imaginary unicorn. Therefore, we can rule out a priori “pile of bricks” as a possible cause of “imaginary unicorn.”
Similarly, the physical chemicals in the brain are incapable of producing the mental images in the mind. There is a vast, unbridgeable ontological gulf between physical things and mental things. Therefore, we can rule out, in principle and a priori “chemicals” as a cause of “thoughts.”
Popperian invariable yells “False! You’ve committed inductivism.” Before we show why Popperian is wrong, let’s get clear what he is talking about. Wikipedia describes the issue as follows:
Generalizing about the properties of a class of objects based on some number of observations of particular instances of that class (for example, the inference that “all swans we have seen are white, and therefore all swans are white”, before the discovery of black swans)
So why is Popperian wrong? Simple, it is not inductivism to assert that things in one ontological category cannot produce effects in another ontological category. For example, the number “seven” cannot cause the smell of roses. The color “orange” cannot cause “pi to fifteen digits.”
And if Popperian were to yell, “False! You are committing inductivism,” we would think he is a loon. This is not the same thing as the black swan error, because we are not inferring a universal principal based upon necessarily limited empirical observations. Instead, our conclusion is grounded in a more fundamental metaphysical foundation: logical possibility (or impossibility as the case may be). In no coherent universe does “seven” cause “smell of roses.” Therefore, this, like all logically impossible statements, can be ruled out on an a priori basis.
But, Popperian, continues, you don’t know that chemicals cannot cause thoughts. It’s possible that they do. This is where Popperian gets “Possible Possum” syndrome. You remember Possible Possum from the old Deputy Dawg cartoons right? His catch phrase was “It’s poss-i-bool; it’s poss-i-bool.” See here.
Well Popperian, that’s not how we do science or metaphysics. If I say we can rule out a priori “pile of bricks” as a possible cause of “imaginary unicorn” because it is logically impossible for a pile of bricks to cause an imaginary unicorn, it is absurd to stamp your foot and say “You’ve committed the error of inductivism, because it’s poss-i-bool; it’s poss-i-bool!”
Bare, unsupported claims of possibility will not defeat my a priori claim. You are the one asserting possibility, so it is your burden to demonstrate possibility by outlining a plausible mechanism for how a pile of bricks could cause an imaginary unicorn. And if you can’t even begin to do so, my claim is unrefuted.
The same goes with my claim that we can exclude “chemicals” on an a priori basis as being a cause of “mental images.” Again, the bare assertion “it’s poss-i-bool; it’s poss-i-bool” gets you nowhere. If you say it’s possible, then show us; until then my claim stands unrefuted.