Reflection on the Mind as the Origin of Metaphysical Concepts in Descartes, Locke, Leibniz, and Kant: An Explanatory Circle in Early Modern Philosophy and Kant’s Qualified Lockeanism

What explains that our concepts possess the representational contents they do, namely, represent whatever they represent? Kant credits Locke’s Essay with first formulating this question about the origin of conceptual content. While the question for the origin of specifically metaphysical concepts, such as and , becomes already pressing with Locke, it was Kant’s reading of Leibniz’s Nouveaux Essais that properly put this problem on Kant’s agenda. I argue that the first Critique’s Metaphysical Deduction of the Categories, in connection with some material from their Transcendental Deduction, constitutes Kant’s answer to this Leibnizian form of the Lockean question for the origin of conceptual content. First, I collect and analyze material from Leibniz, Locke, and Descartes regarding their shared albeit differently elaborated views of reflection on the mind as the source of metaphysical concepts. This leads me to the diagnosis of an explanatory circle common to these early modern views before Kant. Then, I reconstruct how Kant developed a series of insights from his predecessors Descartes, Locke, and Leibniz into his own view of reflection on the understanding as the origin of metaphysical concepts. I conclude that his view can avoid the explanatory circle. In particular, a novel connection of two Lockean thoughts helps yield Kant’s answer to the Leibnizian form of the Lockean question: first, that a reflection on representational acts explains the contents of metaphysical concepts, similar to a Lockean reflection on ideas and operations in inner sense; second, that these acts, more specifically, are acts of combination required for the representation of objects of experience and their features, similar to a Lockean combination of simple into complex ideas. The representational contents of Kant’s categories, as the most fundamental concepts of an object in general, are based on a reflection on acts of synthesis exercised in experiences of objects.