There are some real doozies of arguments that have tied up religious and philosophical thinkers for centuries. Take the Kalam Cosmological Argument or the Ontological Argument. In both of these arguments there is a required reduction of the properties of the universe (or cosmos) to some kind of skeletal representation. In Kalam (and variants) there are assumptions built into the idea of nothingness, for instance, that have no relationship to what we know about the actual cosmos now—specifically that there is no example of such a thing; even in vacuums there are pervasive quantum fields and we have no clear scientific evidence or theories that point to a “philosopher’s nothingness.” In the Ontological Argument, there is the assumption that possibility and existence are inherently combined together, regardless of whether we are talking about a concept of God or a real thing in or supporting the existence of the cosmos. Another example of this philosophical craziness is in the modal argument for the existence of philosophical zombies, where there are people just like us in every way but lacking a phenomenal experience of being conscious beings.
There is a category of thought called “modal skepticism” that argues we should be cautious about making assumptions about things extremely outside of ordinary experience. Whether it’s the properties of gods or nothingness or consciousness, the trouble arises when trying to sketch out the properties that apply to these things. Even before modal logic in its modern form, Kant argued that existence is not a predicate and therefore the existence of God can’t be contained in an a priori definition of God. We are making an incorrect assumption. In Kalam, nothingness is not definable in a way that meaningfully separates it from a posteriori discoveries about the cosmos, where it does not seem to exist. And for phenomenal consciousness a similar problem controls. Substituting a vague or secondary a priori semantics for whatever consciousness actually is doesn’t make the conceivable thing (that the mental and physical are distinct) an actual thing.
This problematic nature of imagining how conceptual structures build semantics in our heads is nicely critiqued by Peter van Inwagen in this quote taken from Strohminger and Yli-Vakkuri’s “Moderate Modal Skepticism“:
In my view, we cannot imagine worlds in which there are naturally purple cows, time machines, transparent iron, a moon made of green cheese, or pure phenomenal colors in addition to those we know. Anyone who attempts to do so will either fail to imagine a world or else will imagine a world that only seems to have the property of being a world in which the thing in question exists […] Can we imagine a world in which there is transparent iron? Not unless our imaginings take place at a level of structural detail comparable to that of the imaginings of condensed-matter physicists who are trying to explain, say, the phenomenon of superconductivity. If we simply imagine a Nobel Prize acceptance speech in which the new Nobel laureate thanks those who supported him in his long and discouraging quest for transparent iron and displays to a cheering crowd something that looks (in our imaginations) like a chunk of glass, we shall indeed have imagined a world, but it will not be a world in which there is transparent iron. (But not because it will be a world in which there isn’t transparent iron. It will be neither a world in which there is transparent iron nor a world in which there isn’t transparent iron)
We need to be cautious about conflating our imaginations with reality, it seems. Any kind of imagined world where the mental and physical are separable is just that, an imaginary world. As is a world where there is a greatest possible being that is, like, super cool and perfect and love. The imagined existence of these things is inherently broken unless it can be imagined in such detail as to become an effective model of the thing imagined. So, per van Inwagen’s notion of transparent iron, we could conceive of nothingness but need to describe it fully by linkages to the ontologies of cosmology, a complex and moving target filled with many theories (note that this is perhaps achievable even though it is quite far afield from everyday existence). For p-zombies, we need to explain exactly how in some possible world complex mental operations that involve reacting, cogitating, reflecting, and responding to unpredictable environmental signals might be done without the existence of phenomenal consciousness which, in turn, requires that we understand exactly how neural and conscious processes coexist and interact in this world (or don’t). Otherwise we are imagining worlds where we build up references to these ideas but the thing itself remains indistinct and incomplete.
“Moderate Modal Skepticism” does critique van Inwagen’s specific argument (derived from Yobli) but nevertheless takes it as representing a method of critique that has an appealing flavor in that it dovetails with general epistemic humility, even about the difficulty of the project itself:
An attitude of epistemic humility, however, seems to us at least as warranted in the epistemology of modality, when it comes to the knowability of the possibility of states of affairs that are distant from actuality. While we have good evidence that many possibility claims of interest to philosophers, including van Inwagen’s paradigms, are difficult to know, we think that epistemic humility should also rein in the temptation to conclude that those claims are unknowable.
Imagining stuff is fine, but we should be cautious around the crazy and even about imagining we know this is the end of the journey.