A distinctive feature of Spinoza's thought is that it rejects any explanatory mechanisms grounded in mystery or de jure unknowability, in particular any explanatory criteria of experience and knowledge that would rely on ‘objects’ external to the mind. While Spinoza concedes that ‘a true idea must agree with its object’, he understands philosophical explanation to be grounded properly not in truth but in adequacy: ‘By adequate idea I understand an idea which, insofar as it is considered in itself, without relation to an object, has all the properties, or intrinsic denominations of a true idea.’ From a Spinozist point of view, then, empiricism in anything like the Lockean style is a philosophical non-starter. For Spinoza, it will never be sufficient to rest any explanation of experience, knowledge or power on the sheer fact that it is given. No doubt one always begins with what is given, but on Spinoza's terms philosophy fails to think adequately if the given functions for it as an answer and not solely as a relative starting-point. Thought itself is a transitive activity and a continuous process, and so beginnings are as such exterior to thought. Because for a philosophy of immanence nothing can be absolutely exterior to thought, such thinking cannot countenance absolute beginnings. Among other reasons this is why the undivided term ‘God, or Nature’ in Spinoza must be understood not as a foundation or ultimate principle but rather as an incontrovertible milieu: real immanence.

If certainly no Lockean empiricist, Spinoza does seem to be grouped readily among the early modern ‘rationalists’. And sure enough, Spinoza shares with Descartes and Leibniz a resolute willingness to blur if not entirely efface the distinction of logic – and mathematics – from metaphysics. For reason as such, conceptual and formal relations, not the experiential contents of the senses, are eminently knowable. Hence metaphysics as the rational science of reality's ultimate structure is feasible. Yet unlike Descartes and Leibniz, Spinoza makes no important contributions to mathematics and indeed demonstrates no exceptional aptitude in that arena.