 Hurley (1998) examines this question in detail, as does Bayne (2010: ch. 9.4). Hurley comes at the question of transitivity by considering some results reported by Sergent (1990). Since Sergent’s work has not been replicable, let us look instead at how the research by Trevarthen that we mentioned in  Section 4.1.6  throws up the same issue. In this research, as we said, brain bisection patients under certain conditions are conscious of some object seen by, say, the right hemisphere until the left hand, which is controlled by the right hemisphere, reaches for it. Somehow the act of reaching for it seems to obliterate the consciousness of it. Very strange—how can something pop into and disappear from unified consciousness in this way? This question leads Hurley to the notion of partial unity. Could two centres of consciousness, A and C, though not unified in consciousness with one another, nonetheless both be unified with some third thing, in this case the volitional system B (the system of intentions, desires, etc.)? If so, ‘being unified with’ is not a transitive relationship—A could be unified with B, and C could be unified with B, without A being unified with C. This idea is puzzling enough. Even more puzzling is how activation of the system B, with which both A and C are unified, could result in the loss of consciousness in A and/or C of an object aimed at by B.