A glance at the tables of categories that have appeared in the course of the history of philosophy, from that of Aristotle, which is the first, at least among the conspicuous, to that of Stuart Mill, or if it be preferred, to the Kategorienlehre of E. von Hartmann, which is the last, or among the last, shows at once that the other categories, which have been described as logical categories, can be reduced to verbal variants of this unique one of the pure concept, or belong to other aspects of the spirit and of reality, as distinct from that of logical thought. For if in the Aristotelian table the _ousia_ and the _poion,_ substance and quality, to some extent denote the subject and the predicate of the judgment, that is to say, the abstract elements of the _a priori_ synthesis: the _poson,_ on the other hand, appeals to the processes of enumeration and of measurement, the _pou_ and the _poté_ to the determination of space and time, the _poiein_ and the _paschein_ to the principles of practical activity, and so on. The Kantian table seems to refer, or to mean to refer, to logical thought; but that does not prevent the appearance in it of traces of the principles of mathematical, naturalistic, heuristic, and other processes. Furthermore, in the Kantian philosophy, the whole system of the categories is to be deduced, not from the transcendental Logic alone, but also from the transcendental Æsthetic (space and time), and from the Critique of Practical Reason and Judgment, which all lead to functions or forms, operating as spiritual syntheses and reappearing as categories in judgments. Finally, we must not neglect the Kantian metaphysical categories of Physics. [Sidenote: _The Hegelian system of the categories and other later systems._]