Alison Hills (2009) argues that we can seek to undermine the case for supervenience by granting that in many cases ethical difference without naturalistic difference seems inconceivable, and arguing that we should not take inconceivability here to be a good guide to impossibility.
"Conceivability or inconceivability is a life's work — it's not something where you just screw up your head for a second!" He feels that Darwin's central lesson — that everything in biology is gradual; that it arrives "not in a miraculous, instantaneous whoosh, but slowly, slowly" — is too easily swept aside by our categorical habits of mind.
The challenge of writing about mass extermination, according to the historian Dan Diner, comes from "the inconceivability, the basic unimaginability of the event itself".
Parmenides has not fallen prey here to the purportedly paradoxical character of negative existential statements but makes a perfectly acceptable point about the inconceivability of what necessarily is not.
We do not have all the conditionality (specifiability, particularity) on one side and all the unconditionality (transcendence, inconceivability) on the other.
Alternatively, some suggest that the inconceivability of zombies awaits the development of new concepts that can provide a link between our current phenomenal and physical concepts (Nagel 1975, 2000), while others (McGinn 1989) agree, but deny that humans are capable of forming such concepts.
Of greater relevance was his suspicion of the move from conceivability to possibility, and inconceivability to impossibility, thinking that answers to questions about conceivability were dependent upon the state of knowledge and imaginative powers of the person entertaining them.
For example, one could argue that inconceivability is a reliable guide to impossibility, while conceivability is a not a reliable guide to possibility.
Herbert Spencer argued that this, the "inconceivability of the contrary," provided the criterion of truth.
For Mill the inconceivability of the opposite in the case of perceptual judgments and judgments of sense was a matter of psychology while the inconceivability of the opposite in the case of logic was a matter of that opposite being inconsistent, which is not a matter of psychology.
Any philosopher with an interest in the relation between conceivability and possibility should be prepared to recognize in Parmenides' assertion that you could neither apprehend nor indicate what is not (and must not be) one of the earliest instances of a form of inference that from inconceivability to impossibility that continues to occupy a central position in metaphysical reasoning.
