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 586 HOLLAND. doctrine of the five sources of knowledge: Sensation, the feeling of pleasure and pain, aesthetic, moral, and relig-. ious feeling. If we build on the foundation of the first three alone, we end in materialism ; if we leave the last unused, we reach positivism ; if we make religious feeling the sole judge of truth, mysticism is the outcome. The criteria of science are utility and progress. These are still wanting in the mental sciences, in which the often answered but never decided questions continually recur, because we have neither derived the principles chosen as the basis of the deduction from an exact knowledge of the phenomena nor tested the results by experience. The causes of this defec- tive condition can only be removed by imitating the study of nature : we must learn that no conclusions can be reached except from facts, and that v/e are to strive after knowledge of phenomena and their laws alone. We have no right to assume an "essence" of things beside and in addition to phenomena, which reveals itself in them or hides behind them. Pupils of Opzoomer are his successor in his Utrecht chair, Van der Wyck, and Pierson. We may also mention J. P. N. Land, who has done good service in editing the works of Spinoza and of Geulincx, and the philosopher of religion Rauwenhoff (1888). On the system of the Hungarian philosopher Cyrill Horvith (died 1884 at Pesth) see the essay by E. Nemes rX.ie Zeiischrift fiir Philosophie, yoX.Vxx^mn. 1886. Since 1 889 a review, Problems of Philosophy and Psychology, has appeared at Moscow in Russian, under the direction of Professor N. von Grot.