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metaphysical doctrine of body ” (4:473)1 in order to show the existence and extent of the proper science of matter. In the Preface, however, Kant argues that both chemistry and “the empirical doctrine of the soul ” fail to be “a properly so-called natural science ” (4:471). The empirical doctrine of the soul falls especially short for two reasons: (1) mathematics is not applicable to its subject matter and (2) unlike chemistry, the empirical doctrine of the soul can never become an “experimental doctrine ” because “the manifold of inner observation...cannot be held separate and recombined at will ” (4:471). In addition to these remarks in the Preface, I will identify another argument – mostly in the Mechanics chapter – against the possibility of a proper science of the soul: because the soul is not permanent, laws of the kind required by proper science cannot even be formulated. Call the argument in (1) the impossibility argument (following (Sturm 2001)) and this later argument the impermanence argument. I will analyze both of these arguments. In so doing, I will explicate just what Kant means by proper science and, in particular, the role of the application of mathematics. Although much of the literature on this aspect of MFNS has maintained that the impossibility argument plays a far more pivotal role than the impermanence argument,2 I will show that a full analysis of th