The epistemic gap and causal closure

In the philosophical literature, the main objection to physicalism about consciousness is the epistemic gap: the alleged fact that full knowledge of the physical does not yield full knowledge of the mental. And one of the main objections to nonphysicalism about consciousness is causal closure: the alleged fact that physical events, like our actions, have causes that are entirely physical.

There is a simple way to craft a theory that avoids both objections. Simply suppose that mental states have two parts: a physical and a non-physical part. The physical part of the mental state is responsible for the mental state’s causal influence on physical reality. The non-physical part explains the epistemic gap: full knowledge of the physical world yields full knowledge of the physical part of the mental state, but not full knowledge of the mental state.

Something Mary doesn't know

Here is something our old friend Mary, raised in a black and white world, cannot know simply by knowing all of physics:

1. What are the necessary and sufficient physical conditions for two individuals to be in exactly the same phenomenal state?

Of course, her being raised in a black and white world is a red herring. I think nobody can know the answer to (2) simply by knowing all of physics.

Some remarks:

• Knowledge of the answer to (1) is clearly factual descriptive knowledge. So responses to the standard knowledge argument for dualism that distinguish kinds of knowledge have no effect here.

• The answer to (1) could presumably be formulated entirely in the language of physics.

• Question (1) has a presupposition, namely that there are necessary and sufficient physical conditions, but the physicalist can’t deny that.

• A sufficient conditions is easy given physicalism: the individuals have the exact same physical state.

• Dennettian RoboMary-style simulation does not solve the question. One might hope that if you rewrite your software, you can check if you have the same qualia before and after the rewrite. But the problem is that you can only really do exact comparisons of qualia that you see in a unified way, and there is insufficient unification of your state across the software rewrite.

Fading knowledge of qualia

I am one of those people who do not have vivid memories of pains.

Suppose I stub my toe. While the toe is hurting, I know what the toe’s hurting feels like. After it stops hurting, for a while I still know what that felt like. But I know it less and less well as my memory fades, until eventually I know very little how it felt like. The whole process might take only a few minutes.

Thus, that mysterious “knowing what it’s like” involving qualia is something that comes with a parameter that varies as to how well you know it.

This should worry physicalists. Thin physicalists should worry because it doesn’t seem that the fading corresponds to any knowledge of the underlying physical reality. Thick physicalists who think that Mary just acquires a new recognitional concept when she sees red should worry, because it does not seem that there is any gradual loss of a concept. I continue to have the same “that experience” concept (the demonstrative “that” points to the same past experience, and does so in a first-personal way) and the recognitional abilities it enables (I can tell if another pain is like that one or not), even as my knowledge of what “that experience” is like fades.

It’s also not completely clear what a dualist should say about the fading of the knowledge. Normally, when knowledge fades, what happens is either that we lose details (as when I forget much of what I once learned in school about the Metis uprising), or we find the dispositional knowledge harder to make occurrent. But the fading is neither of these. Maybe what is happening is that our present knowledge becomes a less good representation of what it is the knowledge of.

Second-order perception and the knowledge argument

Here’s something odd in the knowledge argument as usually formulated. According to the knowledge argument, Mary who was raised in a black and white argument but knew all of science came to know what it is like to see red by seeing red, despite having known all the physical facts first.

But note that one cannot simply come to know what it is like to see red by seeing red. One knows what it is like to see red by having the second-order perception of oneself seeing red. When one has the first-order perception without the second-order one, one doesn’t directly know that one has the first-order perception. (One may be able to infer it, of course: Here is a tomato, my eyes are open and are pointed towards it, so I am seeing it.) Of course, typically when one has the first-order perception, one also has the second-order perception (but typically not the third-order one), but the point remains is that it is not by the first-order perception, but by the second-order one, that one learns what it is like to see red.

Presumably, any ordinary human perception can be mistaken: it can occur in the absence of its object. Thus it is possible to have the second-order perception without the first-order one. It follows that it is possible for Mary to know what it is like to see red without ever seeing red: all she needs is the second-order perception.

This does not seem to me to damage the knowledge argument as such, but merely to tweak it. For even after the above reflection, it still seems plausible that one doesn’t know what it is like to see red on the basis of physical facts, but by means of a second-order perception. Moreover, we now have an answer to the memory objection to the knowledge argument, namely that just as you and I can know what it is like to see red by having true memories of seeing red, so too someone could know what it is like to see red by having false memories of seeing red, and so actual perception of red is not needed. But this does not affect the argument once we have realized it’s about the second-order perception. For memories, true or false, of seeing red are a kind of temporally backwards second-order perception.

More on the non-causal dualist theory of perception

In a recent post, I offered a non-causal dualist theory of sensory awareness on which when I see a red cube, there is a state r_b of my brain representing the red cube, and a relation V of perception between r_b and my soul, which relation is external to the soul. As a result, there need be no intrinsic difference between my soul when I am perceiving red cube and my soul when I am not perceiving a red cube.

I want to make a few more notes on this theory, for it seems to me that it is worth taking seriously.

1. This theory is very close to Aquinas’. Aquinas thought that sensory awareness was constituted by the reception of sensory data (“phantasms”) by sense organs. The sense organs, and not the soul, are modified by the sensory awareness. Of course, it was crucial to this that the sense organs be informed by the form of the animal, and the form of an animal is the soul. So we have a similar structure: there is a relation of the soul and the sense organs, and the sense organs are then modified by the sensory data. If we neglect the difference between the brain in my theory and the sense organs in Aquinas’s, then Aquinas’s theory is just an expansion on my theory. The state r_b is the state of the sense organs having their sensory data, and my external relation V of perception on Aquinas’s view is simply constituted by a pair of relations on Aquinas’s: the informing relation of the soul to the organ, and the sensory-data-possession relation between the organ and its sensory data.

Thus, the main difference between my theory and Aquinas’s is that I replace the sensory organs with parts of the brain. And there is good reason to think that if Aquinas had the empirical data we do, he would think of the phantasms as in the brain rather than in the eyes, ears, etc. For we have good reason to think direct neural stimulation of the visual center of the brain could produce the same visual experience as gazing upon a red cube. Thus, the only difference between Aquinas and the theory—apart from Aquinas offering more detail on the relation V—is that on the theory, the sensory organs in Thomas’s sense are all inside the skull.

2. What we should say about qualia on this theory? The analogue to the visual quale of my perceiving a red cube on this theory consists of V and r_b. That’s a pair of things rather than one thing. One of these two things, the brain state r_b, is physical, but the other thing, the relation V, is a non-physical relation between a non-physical thing, the soul and a brain state r_b. Thus qualia are partly non-physical and partly physical.

3. It seems the theory contradicts the knowledge argument. Consider the brain state r_b representing a red cube and the brain state g_b representing a green cube. It seems that on the basis of seeing a green cube, I can get to know the relation V obtaining between my soul and g_b. And on the basis of neuroscience, I can get to know r_b. Thus, without ever seeing anything red, it seems I can know what it’s like to see red.

I am not strongly attached to the knowledge argument in its standard form. I kind of like the radical variant on which a never conscious person could never get to know what consciousness is like. And that variant fits with the theory, since a never conscious person has never experienced the relation V. (You might say: A never conscious person couldn’t know anything. I think it is a mistake to require consciousness for knowledge. First, one can have non-occurrent knowledge without consciousness—I know my multiplication tables even when asleep. Second, the unconscious vampires in Watts’ Blindsight clearly have knowledge.)

That said, I do not think it is obvious that just by knowing what the ingredients are like one knows what the whole is like. Thus, knowing what r_b and V are like may not be enough to know what it is like to have one’s soul stand in V to r_b. (Compare: Alice knows what it is like to be married to Bob, and she knows Carl, but it doesn’t follow that she knows what it is like to be married to Carl.)