Many experimental findings with split-brain subjects intuitively suggest that each such subject has two minds. The conceptual and empirical basis of this duality intuition has never been fully articulated. This article fills that gap, by offering a reconstruction of early neuropsychological literature on the split-brain phenomenon. According to that work, the hemispheres operate independently of each other insofar as they interact via the mediation of effection and transduction—via behavior and sensation, essentially. This is how your mind and my mind interact (...) with each other, however, giving rise to the intuition that a split-brain subject has two minds. (shrink)