1 An anonymous referee, this journal, asks incredulously: “Only one property? We should be looking for just one!?” While McGinn's main points do not depend on how many such properties there are, it may well strike one as implausible, barring artificial conjunctive properties, that just one property does it all.
2 In a note (p. 3, n. 3) McGinn acknowledges Noam Chomsky, who, in Reflections on Language (Pantheon Books, 1975), pp. 66–67, sketches a plausible evolutionary argument for the general thesis that “… we are subject to biological limitations with respect to the theories we can devise and comprehend,” and further that it is not unintelligible that we might be able to identify particular domains of inaccessibility. But this, if accepted, still leaves open whether consciousness constitutes such a domain. Thanks are due to Peter Loptson for making sure that I actually saw the passages in Chomsky.
3 It is interesting to compare this naturalistic alternative with Thomas Nagel's blatantly antiphysicalistic “dual aspect theory,” in The View from Nowhere (New York: Oxford University Press, 1986), esp. pp. 46–49. Nagel is frequently cited approvingly by McGinn, and in the Preface (p. viii) he pays Nagel this homage: “I doubt if I would have arrived at the present view had I not first been steeped in his ideas.” But according to Nagel, the objective physical and the subjective mental are each irreducible aspects, each manifestations of some more basic and fundamental term of which we currently have no conception. Now there is a structural analogy here: like Nagel, McGinn (on the naturalistic, nomologically necessary connection alternative) would posit P as mediating between, connecting, the straightforwardly physical with the mental, while in some sense being neither. But there is also an important disanalogy: P would not, contra Nagel, be taken to underlie or be more basic than the physical. Ordinary spatial physical properties would remain the most basic for McGinn.
4 A variant of this line that might also be implicit in the text is: only a non-spatial cause of non-spatial consciousness would make it intelligible to us; and there is something that would make it intelligible to us, if only we could grasp it! McGinn considers but rejects a different explanation of our sense of mystery about the psychophysical link, according to which we are not cognitively closed with respect to P, but, in linking brain and consciousness, our epistemic acquaintance with them are mediated, respectively, by the disparate faculties of sensory perception and introspection. Thus even if we were somehow given a concept for the property P, we would still experience an illusion of inexplicability, from the necessity of having to shift from one faculty to the other in order to grasp it. McGinn rejects this explanation, apparently on the grounds that it begs the question as to whether facts can only seem straightforwardly intelligible to us if we apprehend them by a single faculty (cf. pp. 14–15). But we are given so little to go on here that it seems one could just as easily argue that the denial of the explanation begs the same question!
5 McGinn's implicit reply to this is that P is such that, if we could but grasp it, it would, somehow, make perfect sense of the psychophysical nexus; the connections between the physical and P and between P and the mental would be as clear as P itself (cf., e.g., p. 104). But of course we just have McGinn's word on this. Even if he makes it a defining condition of the property he posits, we are given no independent assurances that there is any such property.
6 Thanks to John Pugsley, who first interested me in McGinn's cognitive closure, and to an anonymous referee of this journal for helpful advice.