similar way (viz., by finding a synthesis for apparent contradictions), he deduces the two other categories of this class, viz., that of cause, and that of substance. The process is thus: So far as the Ego is determined, and therefore passive, has the non-Ego reality. The category of reciprocal determination, to which we may ascribe indifferently either of the two sides, reality or negation, may, more strictly taken, imply that the Ego is passive, and the non-Ego active. The notion which expresses this relation is that of _causality_. That, to which activity is ascribed, is called _cause_ (primal reality), and that to which passiveness is ascribed, is called _effect_; both, conceived in connection, may be termed a _working_. On the other side, the Ego determines itself. Herein is a contradiction; (1) the Ego determines itself; it is therefore that which determines, and is thus active; (2) it determines itself; it is therefore that which becomes determined, and is thus passive. Thus in one respect and in one action both reality and negation are ascribed to it. To resolve this contradiction, we must find a mode of action which is activity and passiveness in one; the Ego must determine its passiveness through activity, and its activity through passiveness. This solution is attained by aid of the conception of quantity. In the Ego all reality is first of all posited as absolute quantum, as absolute totality, and thus far the Ego may be compared to a greatest circle which contains all the rest. A definite quantum of activity, or a limited sphere within this greatest circle of activity, is indeed a _reality_; but when compared with the totality of activity, is it also a _negation_ of the totality or passiveness. Here we have found the mediation sought for; it lies in the notion of _substance_. In so far as the Ego is considered as the whole circle, embracing the totality of all realities, is it substance; but so far as it becomes posited in a determinate sphere of this circle, is it accidental. No accidence is conceivable without substance; for, in order to know that any thing is a definite reality, it must first be referred to reality in general, or to substance. In every change we think of substance in the universal; accidence is something specific (determinate), which changes with every changing cause. _There is originally but one substance, the Ego_; in this one substance all possible accidents, and therefore all possible realities, are posited. The Ego alone is the absolutely infinite. The Ego, as thinking and as acting, indicates a limitation. The Fichtian theory is accordingly Spinozism, only (as Jacobi strikingly called it) a reversed and idealistic Spinozism.