Brains, Persons, and Society *** ABSTRACTS    Cervelli, Persone e Società ***ABSTRACTS

Harris Hatziioannou
School of Oriental and African Studies, University of London

The Epistemic Defence Against the Conceivability Argument

 In the Conceivability Argument against materialism, David Chalmers makes extended use of his version of the two-dimensional framework, in order to support the controversial inference from the conceivability of zombies, to their possibility. This inference has been extensively criticized, and Chalmers has responded (e.g. in ‘The Foundations of Two-Dimensional Semantics’) by fine-tuning his account in order to make explicit how conceivability is supposed to act, at the ideal limit, as a reliable guide to possibility. In particular, he has put forward the notions of ideal positive and ideal negative primary conceivability that are supposed to give us, systematically and unambiguously, a priori access to the single space of possible worlds that he admits as a primitive. In this way, Chalmers claims to have established a correspondence between an idealized epistemic notion of conceivability and the (metaphysical) modal notions of possibility and necessity.

Chalmers’s analytical construction and argument have been criticized on a number of fronts, most intensely with regard to issues that concern the semantics on which his account is based and the metaphysical presuppositions that lie behind it. In the present paper, I attempt to block the argument without challenging Chalmers’s semantics, or his metaphysical presuppositions; instead I concentrate on the conceptual architecture that is used to support his framework, trying to establish that it fails to represent the relevant categories in a satisfactory manner. In particular, I question Chalmers’s construal of some of the epistemic notions that he employs, specifically arguing that the notion of primary conceivability that features in the central conceivability claim of the argument has been construed as a metaphysical notion, and not as an epistemic one. As a result, the conceivability (in this sense) of zombies becomes unacceptable to anyone who is not a committed dualist; at the same time, the inference from conceivability to possibility in the second premise of the argument, is rendered tautological, since it seems to be equivalent to the claim that the conceivability of zombies, understood in a sense akin to metaphysical possibility itself, implies their metaphysical possibility. Hence, the Conceivability Argument fails as a refutation of materialism.

My case against the epistemic notions employed by Chalmers rests mainly on two points. First, on the observation that the notion of epistemic possibility on which his construal of conceivability relies (primary conceivability is based on the evaluation of epistemic possibilities) disregards an important feature that, according to our most natural pre-theoretic as well as philosophical understanding, all epistemic modalities possess. This feature is the relative character that epistemic possibility inherently has, and which can be understood as follows: A judgment that a certain sentence is epistemically possible is always relative to a certain body of knowledge that the relevant epistemic agent or community either already possesses or is within their power to attain. (Relative and absolute modalities have been formally defined along these lines by Bob Hale in his ‘Absolute Necessities’.) At the ideal limit, epistemic possibility may be seen as being relative to a body of knowledge that is a priori knowable by an ideal epistemic agent. Such an idealized notion of epistemic possibility might seem, at first sight, to come close to the one that Chalmers exploits in his argument. However, as I argue in my paper, this is not actually the case: the so-called epistemic possibility employed by Chalmers is no longer a merely relative modality, but has ended up encompassing the whole space of logically possible worlds; it thus seems to be better characterisable as an absolute modality, i.e. as a type of possibility that is at least as weak as any other type of possibility. As I argue in my paper, this makes it lose an important aspect of its epistemic character, bringing it much closer to modalities of a metaphysical kind.

The second point on which my argument rests, concerns the way that Chalmers analyses (ideal) judgments of epistemic possibility in terms of maximal epistemic hypotheses about how the world may, for all we know, be. These epistemic hypotheses, or scenarios, which are complete in every respect, thus become fit to play the role Chalmers envisages for them, i.e. to be systematically and unambiguously paired to possible worlds. Against this analysis, I argue that judgments about what is epistemically possible, even idealized ones that feature in philosophical thought experiments, cannot generally be extended until a maximal scenario is completely filled out; a fortiori, they cannot be taken to correspond to possible worlds, which are by definition complete in every respect. And, as I try to show in my paper, in the case at hand, i.e. in contexts such as the one set by the conceivability claim featuring in Chalmers’s argument, the epistemic possibilities that are relevant are not suggestive of any maximal scenario; rather, they should be simply seen as expressions of our uncertainty regarding the right referent of our concept of phenomenal consciousness. Consequently, a notion of conceivability that is based on the evaluation of this kind of epistemic possibilities cannot be taken as a guide to the space of possible worlds.