Discussions of the relation between confessionalization and early modern natural philosophy have tended to focus on the influence of certain theological doctrines characteristic of the different Christian denominations on specific analyses of the material world. By contrast, I would like to argue that an obstacle to formulating all-too general confessionalization claims derives from ecumenical uses of early modern natural philosophy that serve to provide rational grounds for commonly acceptable theological views. One such ecumenical approach can be found in the work (...) of Kenelm Digby. I develop such a line of interpretation by comparing Digby’s argumentative strategy with the argumentative strategies of one of his readers, Gottfried Wilhelm Leibniz, who in his early writings developed a sophisticated version of mechanical philosophy. Leibniz refers to Digby’s analysis of the powers of organisms, and, like Digby, he uses the limits of these powers as arguments for the existence of immaterial, and hence immortal human souls. The convergence between Digby and the early Leibniz on this central theological point can be seen as an outcome of the analysis of our common notions concerning the nature of matter and of the analysis of our common notions concerning the mental capacities of humans. (shrink)