A bit of epiphenomenalism this morning:
The modal argument (stripped of the creativity and imagination about all possible modalities) says that no amount of physical information about another person will tell you if they are conscious at all. But why should we think that’s true? The claim is not an argument, but a claim, an intuition. This is important. If anyone had shared the intuitions and doubts them now or doubted them later, this is evidence the intuition is doubtful, or least evidence for concern. Modal logic and the Modal Argument for Dualism receives a lot attention and praise for being imaginative, yet at its beating heart, this is how fragile the modal argument is.
A common modal strategy says that if supervenience is not necessary, then physicalism is necessarily false. This is an acceptable strategy, yet dualists like Kripke–who originally advanced the modal argument for dualism–argued that in Naming and Necessity by begging our intuitions to accept the anti-supervenience argument. Zombies, for example, are said logically possible. That is, they’re just like us physically, but have no inner and conscious experiences. That certainly sounds possible. But this isn’t a strong argument against the claim that everything that is physically identical is mentally identical by definition. Or everything that is physically identical must give rise to the same aesthetic experiences in the same person. It’s an intuition that they are possible scenarios.
“That seems possible,” provides no other analysis, however. Daniel Dennet rightly says that these kinds of arguments are intuition-pumping, in that they simply ask us to reflect upon our own intuitions to see if this claim is true or false. If we share the intuition, then the claim will seem true to us. And if we do not share the intuition, the claim will seem false.
Still, if zombies are possible, then physicalism is false, since on the physicalist account, nothing like a zombie should exist, or more precisely, possibly exist. So the correct line of argument for the physicalist is to show that zombies are not, in fact, possible. However, these claims are to be based on the arguments put forth by physicalists themselves, which are much more technical and rely on advances in neuroscience, not based on an intuition that it is possible that a counter-scenario may exist.