In the previous section, we showed how the disjunctive view undermines both the zombie and the anti-zombie arguments for anti-physicalism and physicalism respectively. This also constituted an indirect argument in favour of the disjunctive view of consciousness, showing that it deserves a place alongside the more traditional theories in metaphysics of consciousness. But showing that the two arguments in question are not successful is not the only interesting advantage of the disjunctive view. By appealing to the main tenets of this account, we can formulate versions of physicalism and anti-physicalism that are compatible with the idea that zombies and anti-zombies are both conceivable and metaphysically possible. The aim of this section is to sketch two such views.
The core idea here is that of a Bizarro twin. Bizarro twins are pairs of entities that are nearly physical duplicates, where the exception to exact duplication concerns the physicality or the non-physicality of the twin’s consciousnesses. More precisely:
Bizarro twins: x is a Bizarro twin of a phenomenally conscious creature y if and only if:
if y has only physical and physically-realized properties, then:
x possesses NPC; and,
x is otherwise a physical duplicate of y;
if y’s phenomenal consciousness is a non-physical property, then:
x possesses PPC; and,
x is otherwise a physical duplicate of y.
Although this may look relatively complicated, the idea is in fact straightforward: whatever type of consciousness property one has, one’s Bizarro twin has the other. So, if my consciousness is an instance of a physical property, my Bizarro twin’s consciousness is an instance of a non-physical property; conversely, if my consciousness is an instance of a non-physical property, then my Bizarro twin’s consciousness is an instance of a physical property. Other than this difference, Bizarro twins share all of their physical properties.Footnote 25 We have already encountered a pair of Bizarro twins: A and B in SCENARIO-1 above.
An initial objection to the idea of a Bizarro twin might go as follows. If A has PPC, then A’s Bizarro twin must also have PPC, in which case the very conception of a Bizarro twin is incoherent. After all, if the physical properties of A are duplicated in A’s Bizarro twin, the physical properties that realize PPC will be duplicated in A’s Bizarro twin too, in which case these properties should bring about an instance of PPC. We think this objection is mistaken. When we say that A’s Bizarro twin lacks PPC, we mean to say that it lacks the cluster of physical properties that “PPC” picks out, and these include the physical realizers of A’s consciousness. By analogy, think about a green cereal bowl which has a nearly physical duplicate that is qualitatively identical with respect to all of its physical properties other than its greenness (e.g., because the near duplicate bowl is purple). When we are physically duplicating a green bowl with the exception of its greenness (to render a purple near-duplicate), we simply leave out the minimal cluster of properties that its greenness supervenes on (and we replace that cluster with the ones that deliver purpleness). Clearly, the conception of two cereal bowls that are exactly physically alike except for their colours is coherent; so the conception of Bizarro twins is coherent too.
Now, suppose that the disjunctive view is true, and, moreover, that the only consciousness-grounding property that is, was, and will ever be actually instantiated is PPC. In this case, NPC would be an alien property: a property instantiated in some non-actual world but not instantiated in the actual world. Intuitively, that there are alien non-physical properties ought to be compatible with physicalism. After all, physicalism is often taken to be a contingent thesis. That NPC is an alien property fits nicely with the idea that physicalism may actually be true despite the merely possible instances of NPC.Footnote 26
This notion of a Bizarro twin gives physicalists a new way to accommodate their opponents’ zombie intuitions, as the physicalist can offer an error theory along the following lines. When the anti-physicalist allegedly conceives of a zombie twin of an actual conscious creature x, what she is in fact conceiving of is a zombie twin of a Bizarro twin of x. Granting that conceivability entails metaphysical possibility, this means that zombies are both conceivable and metaphysically possible. But, importantly, this does not show that physicalism is actually false; it only shows that physicalism is possibly false.
Suppose that physicalism is actually true, and A, like all conscious creatures in the actual world, is conscious in virtue of possessing PPC. Suppose further that an actual anti-physicalist says that she can conceive of A’s zombie twin, and from this, she infers that this zombie twin is metaphysically possible. Our would-be physicalist can say that the anti-physicalist is mistaken: strictly speaking, she cannot conceive of A’s zombie twin (in any possibility-entailing sense), for there is no sense in which we can think of a physical duplicate of A that lacks PPC. But the anti-physicalist is not completely off base—there is a nearby zombie twin that can be conceived in a possibility-entailing sense. For in some non-actual world, A has a Bizarro twin, B, who is a near physical duplicate of A, while the only difference is that B has NPC instead of PPC. And it is easy to conceive of B’s zombie twin, C, which physically duplicates B, but lacks NPC, and hence lacks consciousness. But C is not a zombie twin of A, because it lacks a physical property (PPC) that A possesses.
Bringing all this together, our physicalist can say that what the anti-physicalist is doing is mistaking conceiving of A’s zombie twin, which is not a possible being, with B’s zombie twin, which is a possible being. Further, this physicalist can grant that zombies are conceivable (provided one is careful about what exactly it is they are conceiving) and also metaphysically possible.
This variant of physicalism, which we call Bizarro physicalism, consists of the following commitments:
All actually instantiated non-disjunctive properties are physical (or physically-realized), including all actual instances of consciousness.
In some (merely) possible worlds, consciousness is instantiated in virtue of a non-physical property.
The conceivability of zombies entails the possibility of zombies.
Zombie twins of actual conscious creatures are neither conceivable nor metaphysically possible.
Zombie twins of Bizarro twins of actual conscious creatures are both conceivable and metaphysically possible.
As (1) suggests, qua physicalists, Bizarro physicalists accept that all actually instantiated non-disjunctive properties are physical (or physically-realized). This goes to show the compatibility of Bizarro physicalism with a typical physicalist claim that any minimal physical duplicate of the actual world is a duplicate simpliciter.
Bizarro physicalism is a modest view in the sense that it claims that consciousness is only contingently physical. But it is a bold view in that it denies that zombie twins of actual conscious creatures are conceivable in a possibility-entailing sense. Moreover, it has a very desirable feature: it explains the temptation to think that zombies are both conceivable and metaphysically possible. After all, zombies are conceivable and metaphysically possible. But the zombies that are conceivable and metaphysically possible are not our zombie twins; rather, they are the zombie twins of our Bizarro twins. One might say that they are our “zombie cousins”.
At the end of §4, we said that a pressing version of the zombie argument, i.e., the version that is formulated in terms of zombie worlds, needs still addressing. Having now introduced the concept of a Bizarro twin, we can finally tackle this argument—or at least show how the Bizarro physicalist can tackle it. To make the argument explicit, we ask you to consider a die-hard zombie fan who is unmoved by our case against the original zombie argument which appeals to SCENARIO-4, which concerns individual creatures. But zombie arguments can be, and often are, run in terms of entire worlds rather than individual creatures. So, our die-hard zombie fan could argue that an entire zombie world – i.e., a world that features zombie twins of all actual conscious entities – is conceivable, and hence possible; this would get around our SCENARIO-4 argument, leaving the world-based zombie argument intact.
But note that, in response to the world-based zombie argument, a Bizarro physicalist can reply that the zombie world that is considered in this argument does not feature our zombie twins – rather, it concerns the zombie twins of our Bizarro twins. That is, the zombie world is metaphysically possible, and is also conceivable, though not in the manner that the zombie theorist originally hoped for. This is enough to undermine the argument, leaving the (Bizarro) physicalist able to maintain their distinctive brand of physicalism.Footnote 27
The notion of Bizarro twins also helps us formulate a novel version of anti-physicalism. Suppose that the disjunctive view is true, and moreover, as a matter of fact, the only consciousness-grounding property that is, was, and will ever be actually instantiated is NPC. Allowing for Bizarro twins gives the anti-physicalist an easy way to accommodate physicalists’ talk of the conceivability (and hence possibility) of anti-zombies: if A is an actual conscious creature, then A’s Bizarro twin B is also A’s anti-zombie twin. That is because B will have (i) all of A’s physical properties, (ii) lack NPC, but (iii) possess PPC. Of course, this argument assumes that we define anti-zombies as bare physical duplicates (i.e., they must have at least all the original creature’s physical properties, but can have more physical properties too).
If we define anti-zombies in terms of minimal physical duplicates (so, they have all the original physical properties and nothing further), then we have to slightly complicate the story in a way that parallels the Bizarro physicalist account above. Specifically, let A be an actual creature that has NPC. Let B be A’s Bizarro twin, and C be a minimal physical duplicate of B. C will not be a minimal physical duplicate of A, since C has PPC, which A lacks. This means that C is not an anti-zombie twin of A. So, paralleling the account above, the anti-physicalist can say that anti-zombie twins of actual non-physically conscious individuals are neither conceivable nor possible. However, the conceivability and possibility of C—i.e., an anti-zombie twin of a Bizarro twin—explains why a physicalist might mistakenly think they are.
The upshot is a position that mirrors Bizarro physicalism: consciousness is actually non-physical, anti-zombies are conceivable and therefore metaphysically possible, but anti-zombie twins of actual non-physically conscious creatures are not possible. What explains the mistaken thought that they are conceivable and possible is the fact that anti-zombie twins of Bizarro twins are both conceivable and possible.
Bizarro anti-physicalism is also a modest view in the sense that it claims that consciousness is only contingently non-physical. But it is a bold view, in that it denies that anti-zombie twins of actual phenomenally conscious creatures are conceivable in any possibility-entailing sense. Moreover, it has a very desirable feature: it explains the temptation to think that anti-zombies are both conceivable and possible; they are conceivable and possible after all. But the anti-zombies that are conceivable and possible are not our zombie twins; rather, they are the anti-zombie twins of our Bizarro twins—our “anti-zombie cousins”, if you will.Footnote 28