This thesis presents an interpretation of Immanuel Kant’s theoretical philosophy in which the notion of ‘force’ is of central importance. My analysis encompasses the full span of Kant’s theoretical and natural-scientific writings, from the first publication to the drafts of an unfinished final work. With a close focus on Kant’s texts, I explicate their explicit references to force, providing a narrative of the philosophical role and significance of force in the various periods of the Kantian oeuvre. This represents an intervention (...) into Kant scholarship that seeks to correct the marginal role accorded to ‘force’. The central problem that emerges through the thesis’ attention to force is: how to interpret the simultaneous separation and connection of physical and psychological forces in Kant’s mature, critical philosophy? Physical and psychological forces are strictly separated, and yet a common, ontological conception of force underpins these two domains. I show that this issue has its basis in a tradition of philosophical ‘dynamics’ stemming from Leibniz, which is examined in part one. The three parts of the thesis proceed chronologically through the Kantian oeuvre. Part one reconstructs the historical context of Leibnizian and Newtonian conceptions of force, and presents a narrative of the employment of force in Kant’s pre-critical writings, in their relation to the broad problematic of Leibniz’s dynamics. Part two explores the account of physical and psychological forces, and the common, ontological notion of force, in the major critical-period discussions. Part three presents the late works, namely the third Critique and the Opus postumum, as a ‘philosophy of force’, in which force, with all its necessary ambiguities, plays central roles in Kant’s late systematising endeavours. I conclude that the perspective of this thesis makes possible a new understanding of the nature and unity of Kant’s philosophical project. (shrink)