ABSTRACT
Einstein's rationalist orientation received full public expression for the first time in the Herbert Spencer lecture, "On the Method of Theoretical Physics", delivered at Oxford on June 10, 1933. Einstein's "believing rationalist" is neither a Platonist, nor really a rationalist at all, at least as that term is understood within the tradition stemming from Descartes, Spinoza, and Leibniz. The message that Einstein came to understand as "the truly valuable in Kant" lay in the doctrine of the regulative principles of reason, according to which the very concept of an order of nature presupposes a decision to seek unity through systematic connections. Einstein's last documented discussion of Kant concludes with a reminder that he naturally dissents from the doctrine of a priori categories in the "Transcendental Analytic". A legacy of unification in physical theory still linked to Einstein survives, the attenuated rationalism behind his own attempts might be better, and more productively, understood.
