Conceivability Arguments for Dualism, Part I: Stoljar's Critique of Frank Jackson's Argument

Notes on Daniel Stoljar's “Two Conceptions of the Physical” (PPR, 2002)

This paper is a critique of Jackson’s Knowledge Argument. It distinguishes two conceptions of physical properties: theoretical physical properties (t-physical properties) and intrinsic, categorical, physical properties (o-physical properties). The t-physical properties are exactly those properties dictated to us by physical theory. They are all dispositional, extrinsic, relational properties. The o-physical properties are exactly those properties that are required to give a complete account of the intrinsic, categorical properties of physical objects. The two categories are not co-extensive, as o-properties are intrinsic, and t-properties are not.

Stoljar uses this distinction to construct a dilemma against the Knowledge Argument, the latter of which can be stated as follows:

1. It is possible to know all of the physical facts about seeing red and yet not know all the facts about seeing red.
2. If it is possible to know all of the physical facts about seeing red and yet not know all the facts about seeing red, then physicalism is false.
3. Therefore, physicalism is false.

Stoljar’s dilemma runs as follows:

1. Either “the physical facts” are to be read throughout the argument as “the t-physical facts” or as “the o-physical facts”.
2. If they are to be read as “the t-physical facts”, then although the argument is valid, we have no reason to think it is sound. For the extra facts about what it is like to see red may be o-physical facts, in which case premise (2) would be false.
3. If they are to be read as “the o-physical facts”, then although the argument is valid, we have no reason to think it is sound. For we can’t rule out that knowledge of the o-physical facts, together with knowledge of the t-physical facts, would enable a person to know all the facts about seeing red, in which case premise (1) would be false.
4. Therefore, either way, we have no reason to think that the knowledge argument is sound.

In short, the knowledge argument fails by falsely assuming that knowledge of the physical facts is exhausted by knowledge of the t-physical facts.