 The Story. It will be helpful to sketch the narrative arc before becoming immersed in the details of individual systems. There are two significant shifts that will emerge in the discussion below. The first is the one I’ve already indicated: the transition from moral conscience to a purely psychological concept of consciousness—a move from shared knowledge to a notion of consciousness as what is privately introspectable. This starts with Descartes and, in England, with the Cambridge Platonists. While this is certainly a major development, the central concept remains largely unanalyzed. The second shift occurs later in the seventeenth century, when philosophers start to see consciousness as itself something to be explained. This latter transition begins with the Cartesian philosophers who say more about the nature of consciousness in their development of Descartes’s system and in order to avoid some of the objections raised against it. But for the most part these Cartesians remained committed to consciousness as a fundamental property of the mind, a “mark of the mental.” Leibniz completes this second transition by arguing that consciousness cannot be a mark of the mental. He develops an account of mental representation and provides an analysis of consciousness in terms of mental representations, arguing that this results in a fully natural explanation for something that was otherwise mysterious. This represents the start of an explanatory project that continues to this day: can consciousness be explained in terms of something more fundamental?