Wolff reaches his division of the sciences by combining the two psychological antitheses—the higher (rational) and lower (sensuous) faculties of cognition and appetition. On the first is based the distinction between the rational and the empirical or historical method of treatment. The latter concerns itself with the actual, the former with the possible and necessary, or the grounds of the actual; the one observes and describes, the other deduces. The antithesis of cognition and appetition gives the basis for the division into theoretical and practical philosophy. The former, called metaphysics, is divided into a general part, which treats of being in general whether it be of a corporeal or a spiritual nature, and three special parts, according to their principal subjects, the world, the soul, and God,—hence into ontology, cosmology, psychology, and theology. The science which establishes rules for action and regards man as an individual being, as a citizen, and as the head or member of a family, is divided (after Aristotle) into ethics, politics, and economics, which are preceded by practical philosophy in general, and by natural law. The introduction to the two principal parts is furnished by formal logic.
Philosophy is the science of the possible, i.e., of that which contains no contradiction; it is science from concepts, its principle, the law of identity, its form, demonstration, and its instrument, analysis, which in the predicate explicates the determinations contained in the concept of the subject. In order to confirm that which has been deduced from pure concepts by the facts of experience, psychologia rationalis is supplemented by psychologia empirica, rational cosmology by empirical physics, and speculative theology by an experimental doctrine of God (teleology). Wolff gives no explanation how it comes about that the deliverances of the reason agree so beautifully with the facts of experience; in his naïve, unquestioning belief in the infallibility of the reason he is a typical dogmatist.
A closer examination of the Wolffian philosophy seems unnecessary, since its most essential portions have already been discussed under Leibnitz and since it will be necessary to recur to certain points in our chapter on Kant. Therefore, referring the reader to the detailed accounts in Erdmann and Zeller, we shall only note that Wolff's ethics opposes the principle of perfection to the English principle of happiness (that is good which perfects man's condition, and this is life in conformity with nature or reason, with which happiness is necessarily connected); that he makes the will determined by the understanding, and assigns ignorance as the cause of sin; that his philosophy of religion, which argues for a natural religion in addition to revealed religion (experiential and rational proofs for the existence of God, and a deduction of his attributes), and sets up certain tests for the genuineness of revelation, favors a rationalism which was flexible enough to allow his pupils either to take part in orthodox movements or to advance to a deism hostile to the Church.
Among the followers of Wolff, Alexander Baumgarten (1714-62) deserves the first place, as the founder of German aesthetics (Aesthetica, 1750 seq.). He perceives a gap in the system of the philosophical sciences. This contains in ethics a guide to right volition, and in logic a guide to correct thinking, but there are no directions for correct feeling, no aesthetic. The beautiful would form the subject of this discipline. For the perfection (the harmonious unity of a manifold, which is pleasant to the spectator), which manifests itself to the will as the good and to the clear thinking of the understanding as the true, appears—according to Leibnitz—to confused sensuous perception as beauty. From this on the name aesthetics was established for the theory of the beautiful, though in Kant's great work it is used in its literal meaning as the doctrine of sense, of the faculty of sensations or intuitions. Baumgarten's pupils and followers, the aesthetic writer G.F. Meier at Halle, Baumeister, and others, contributed like himself to the dissemination of the Wolffian system by their manuals on different branches of philosophy. To this school belong also the following: Thümmig (Institutiones Philosophia Wolfianae, 1725-26); the theologian Siegmund Baumgarten at Halle, the elder brother of the aesthete; the mathematician Martin Knutzen, Kant's teacher;[1] the literary historian Gottsched [2] at Leipsic; and G. Ploucquet, who in his Methodus Calculandi in Logicis, with a Commentatio de Arte Characteristica Universali appended to his Principia de Substantiis et Phaenomenis, 1753, took up again Leibnitz's cherished plan for a logical calculus and a universal symbolic language. The psychologist Kasimir von Creuz (Essay on the Soul, in two parts, 1753-54), and J.H. Lambert,[3] whom Kant deemed worthy of a detailed correspondence, take up a more independent position, both demanding that the Wolffian rationalism be supplemented by the empiricism of Locke, and the latter, moreover, in anticipation of the Critique of Reason, pointing very definitely to the distinction between content and form as the salient point in the theory of knowledge.
[Footnote 1: Benno Erdmann, M. Knutzen und seine Zeit, 1876.]
[Footnote 2: Th. W. Danzel, Gottsched und seine Zeit, 1848.]
[Footnote 3: Lambert: Cosmological Letters, 1761; New Organon, 1764; Groundwork of Architectonics, 1771. Bernoulli edited some of Lambert's papers and his correspondence.]
Among the opponents of the Wolffian philosophy, all of whom favor eclecticism, A. Rüdiger[1] and Chr. Aug. Crusius,[2] who was influenced by Rüdiger, and, like him, a professor at Leipsic, are the most important. Rüdiger divides philosophy according to its objects, "wisdom, justice, prudence," into three parts—the science of nature (which must avoid one-sided mechanical views, and employ ether, air, and spirit as principles of explanation); the science of duty (which, as metaphysics, treats of duties toward God, as natural law, of duties to our neighbor, and deduces both from the primary duty of obedience to the will of God); and the science of the good (in which Rüdiger follows the treatise of the Spaniard, Gracian, on practical wisdom). Crusius agrees with Rüdiger that mathematics is the science of the possible, and philosophy the science of the actual, and that the latter, instead of imitating to its own disadvantage the deductive-analytical method of geometry, must, with the aid of experience and with attention to the probability of its conclusions, rise to the highest principles synthetically. Besides its deduction the determinism of the Wolffian philosophy gave offense, for it was believed to endanger morals, justice, and religion. The will, the special fundamental power of the soul (consisting of the impulses to perfection, love, and knowledge), is far from being determined by ideas; it is rather they which depend on the will. The application of the principle of sufficient reason, which is wrongly held to admit of no exception, must be restricted in favor of freedom. For the rest, we may note concerning Crusius that he derives the principle of sufficient reason (everything which is now, and before was not, has a cause) and the principle of contingency from the principles of contradiction, inseparability, and incompatibility, and these latter from the principle of conceivability; that he rejects the ontological argument, and makes the ground of obligation in morality consist in obedience toward God, and its content in perfection. Among the other opponents of the Wolffian philosophy, we may mention the theologian Budde(us)[3] (Institutiones Philosophiae Eclecticae, 1705); Darjes (who taught in Jena and Frankfort-on-the-Oder; The Way to Truth, 1755); and Crousaz (1744).
[Footnote 1: Rüdiger: Disputatio de eo quod Omnes Idea Oriantur a Sensione, 1704; Philosophia Synthetica, 1707; Physica Divina, 1716; Philosophia Pragmatica, 1723.]
[Footnote 2: Crusius: De Usu et Limitibus Principii Rationis, 1743; Directions how to Live a Rational Life (theory of the will and of ethics), 1744; A Sketch of the Necessary Truths of Reason, 1745; Way to the Certainty and Trustworthiness of Human Knowledge, 1747.]