Philosophers of mind talk a lot about zombies. I want to introduce a related species of philosophical monster, which I shall call jekylls. Like zombies, jekylls are atom-for-atom duplicates of us, inhabiting a world with the same physical laws as ours — a world which, let’s assume, is causally closed. Your jekyll twin has all the same physical and functional states you do, including mental ones. It has the same functionally defined perceptions, sensations, thoughts, desires, memories, and emotions, and it is conscious in a functional way too. It also has a sense of self, built of memories, emotions, and introspective and interoceptive states — all functionally defined. (For simplicity, I’ll use ‘psychological’ as David Chalmers does in TCM to mean ‘psychological in a functional sense’.)
So far, then, jekylls are just like zombies. There is a difference, however. Jekylls also have phenomenal states, understood as qualitative mental states that can’t be characterized in functional terms. The phenomenal lights are on inside, as they supposedly are in us. But jekylls aren’t just like us, either. For their phenomenal states are not aligned with their psychological ones. There is a deep incongruity between what they are thinking and feeling psychologically and what they are thinking and feeling phenomenally. When they are psychologically calm, they are filled with phenomenal rage, when they are in psychological pain, they feel phenomenal bliss, when they are psychologically confused, they experience phenomenal clarity, and so on. They are phenomenal/psychological self-inverts.
As a consequence, jekylls have dual selves (you see now why I chose the name). As psychological beings, they have no introspective access to their body’s phenomenal states (which have no distinctive effects), and their phenomenal states make no contribution to their psychological sense of who they are. The subject of their phenomenal states — whatever it is — is completely isolated from the self manifested in their reactions, overt and covert. Each jekyll harbours a phenomenal Mr Hyde. (As with zombies, the literary parallel is not exact, since jekylls never morph into hydes; their inner hyde is forever locked away in a metaphysical limbo.)
Are jekylls conceivable? If zombies conceivable, then jekylls are too. We can conceive of zombies because there is no conceptual connection between functional facts and phenomenal facts. And if there no conceptual connection between functional facts and phenomenal facts, then jekylls are conceivable too. If you think that jekylls are not conceivable, then you have a conception of the phenomenal that is not the one employed in the zombie argument.
Now if phenomenal realism is true, then we are like jekylls, except that our phenomenal selves are beautifully aligned with our psychological ones. You, too, have an ineffective hidden self, but it perfectly mirrors the worldly self manifest in your reactions.
But wait a minute! How do you know that aren’t a jeykll — that you don’t harbour an inner hyde? If you are sure you don’t, then there are two explanations. The first is that you identify with your phenomenal self rather than your psychological one, and know that you are not a hyde. Your mind harmonizes perfectly with the psychological mind your brain processes implement. The downside of this option is that you are strangely alienated from the self manifest in your reactions. You are a phenomenal ghost ineffectively haunting a psychological machine. The other explanation is that at heart you identify with your psychological self and don’t really think you have a phenomenal self at all. You are a complex psychological being, and if you are tempted to think you have a phenomenal self as well, that’s due to features of your psychology. The downside of this is . . . you’re an illusionist!