On an Unpublished Manuscript of Leibniz: New Light on the Vinculum Substantiale and the Correspondence with Des Bosses Brandon Look Department of Philosophy University of Kentucky Explaining the nature of composite substance always posed a challenge for Leibniz. In this paper, I shall provide a transcription, translation and interpretation of an unpublished text in which Leibniz considers the issue of composite substance and the real unity of monads. i While the manuscript has not yet been dated by those working in the Leibniz-Archiv, given that Leibniz discusses the issues in the way he does, the text must have been written between the years of 1712 and 1716. Indeed, this text is, to my mind, particularly fascinating precisely because it echoes certain themes in Leibniz‘s correspondence with Des Bosses, themes that have traditionally piqued the interest of Leibniz scholars and that have generally been thought to be confined to the Leibniz-Des Bosses correspondence. I should like to offer two possible readings of this manuscript. The ―weak‖ reading is simply that this manuscript is some kind of working draft for a 1712 letter to Des Bosses; the ―strong‖ reading is that this manuscript shows an independent explanation of the real unity of composite substance that is so much like the explanation of the vinculum substantiale that we ought to recognize that Leibniz‘s doctrine of the