Bob asked:

There is a tenet still held by some philosophers which is: “Anything that can be imagined is possible”. This was, of course, the basis of Anselm’s ontological argument. My question: What is the formal name of that tenet?

Answer by Craig Skinner

This is called the conceivability argument.

Such arguments are advanced against physicalism, the doctrine that the physical world is all that exists, and that mental states are just physical brain states or aspects of these.

The two best known conceivability arguments are the inverted spectrum argument and the zombie argument.

The inverted spectrum argument says that, for all we know, the sensations you have when looking at colours are the inverse of mine. So, looking at grass, you have the sensation I have when looking at ripe tomatoes, and, looking at ripe tomatoes, you have the sensation I have looking at grass. Of course we both call grass green and tomatoes red, having been so taught, so that there is no communication problem. The argument assumes healthy humans, not people with colour blindness or jaundice.

The zombie argument says that we can conceive of an atom-for-atom duplicate of you, with exactly the same brain states as you, behaving exactly as you, but without any consciousness at all.

So, we can conceive brain states occurring with a mental accompaniment different from usual, or with no mental state at all.. Hence (goes the conceivability argument), whatever causes mental states, they are not wholly determined by brain states, hence physicalism is false.

I think these are poor arguments. I have two objections.

First, conceivability doesnt necessarily mean possibility. Our imagination can outrun possibility. So, the “tenet”, as you term it, is false. Right now, I can conceive my cat jumping up and typing the rest of this answer. But this is metaphysically impossible. There could of course be worlds in which cat-like creatures with superior intelligence do such things, but they would not be cats.

Secondly, advances in our understanding may show that the arguments contain conceptual confusions. Two conceivability arguments that might have been advanced in the 19th Century illustrate this:

  1. We can conceive of a container of gas in which the particles move faster and faster but the temperature of the gas doesnt rise. So, whatever temperature is, it’s nothing to do with particle velocity, right? Wrong, temperature just IS mean particle velocity.
  2. We can conceive of a world containing tiny, replicating, self-stabilizing bags of chemicals undergoing complex interactions (let’s call them ‘cells’) but these cells are not alive, just little bags of dead chemicals. So, whatever life is, it’s not explained by complex chemical interactions. Again, wrong. Life just IS complex interactions of dead chemicals in units drawing energy from outside, maintaining dynamic stability and replicating.

So, I think the spectrum and zombie arguments may likewise fall to advances in cognitive science as we learn how particular brainstates necessarily entail, say, seeing red or being conscious. Meantime, I would say these arguments imagine things that are not possible.