This morning I stumbled upon David Rosenthal’s forthcoming Philosophical Issues paper “How to Think About Mental Qualities” (available on his website). In this paper he argues that inverted qualia are inconceivable. He says,

Quality spaces cannot be symmetrical around any axis without making it impossible to distinguish qualities on one side of the axis from qualities on the other. And [our higher-order awareness] makes one aware of mental qualities in respect of their relative position in the relevant quality space. So that lack of symmetry carries over to the way the [higher order states] make us aware of mental qualities. Undetectable quality inversion is accordingly no more possible for conscious than for non-conscious mental qualities.

The first part of the argument is supposed to show that the usual move, that if saying that the quality space is conceivably symmetrical, for principled reasons about the way perception works. Any quality space complicated enough to do justice to human discriminatory capabilities will have to be asymmetric. This means that any inversion will be detectible from the third person and so quality inversion without detection is inconceivable. The intuition that it is conceivable is a reflection of one’s already accepting what Rosenthal calls a “consciousness-based” theory of the mental qualities. I am deeply sympathetic to this line of argument but I think that there is a problem with Rosenthal’s line of argument in the above passage.

Suppose that we grant the point about the asymmetric quality space, and that the content of the higher-order awareness is also asymmetric. Suppose that in both you and I when we are presented with an orange stimulus the same first-order sensory quality is produced and that this quality is more like the quality that represents yellow and red than it is like the one that represents green and blue, etc. But now suppose that in you there are higher-order thoughts that accurately reflect these similarity and differences. So in you, when the orange quality is consciousness, one has a higher-order state that picks it out as more similar to the yellow* and red* qualities than it is to the green* and blue* qualities. All along, though, we may suppose, in me the ‘opposite’ is happening. When I have a first-order quality that represents orange my higher-order awareness picks it out as the one that is more like green* and blue* than it is like yellow* and red*. But suppose also that I have the same perceptual thoughts that you do. So, I believe that there is something orange near me when I have orange* qualities and when that thought is conscious I consciously believe that something orange is near me. But what it is ike for me in this situation will be like it is for you when you see blue. So we have different conscious experience that is not detectable from a third-person standpoint. We may suppose even that when I introspect my third-order thoughts “get it right”. So, when I introspect my higher-order awareness that the quality is more like green than it is like orange, I am aware of it as one that has the quality more like yellow than it is like green. Thus my introspective reports will exactly match yours. I will also match you in all of my discriminatory abilities.

Granted that this is detectable in principle since we are stipulated to have different higher-order states, which could ultimately be detected in some very advanced neuroscience, but it is nearly undetectable and this is all we need t ground the intuition. In short, it takes a lot of work, even on a purely physicalist conception of the mind like quality space and higher-order theory, to show that these scenarios are not ideally conceivable. Whether they are or not it is important to see that they seem conceivable and that this allows us to get a common sense handle on what we are talking about.