quence between the 'Seinsmomenten' of substance. Accordingly, there would be neither in substance nor in modi a principle of change. The second view conflicts with a formalistic explanation of substance in Spinoza's system. There is only one way to avoid this difficulty. As Schopenhauer employs the will as the creative principle in the world, while in and for itself it is fixed and unchangeable, so with Spinoza the thinking understanding. Schopenhauer (id., S. 32) in his criticism of Wolf’s notion of causa essendi is under a further misunderstanding. This criticism is seen to be erroneous, when we translate into Wolfian language the relation between cause and effect. Wolf in his ontology teaches that simple substances are endowed with forces. Every force consists in the continuous tendency to work, to produce change; the essence of simple substances consists in activity. These force-units, which are the vehicles of objective reality, from the fact of being indivisible and unextended, are to be identified neither with the property of extension nor with that of motion. The specific character of the reacting of force-units Wolf conceived as causa essendi.
Many contradictory world-conceptions obtained following during the time in which Tetens wrote. Central among these was that of the Wolfian school, opposed by the Empiricists and the theological Crusians, and surrounded by the Eclectics, Materialists, Skeptics, and Popular-philosophers. Tetens is distinguished from the Leibnitz-Wolfian school by his treatment of sensation, presentation, and the 'faculties.' He accepts 'unperceived presentations' as the active source of psychical life, but restricts the term 'presentation' to "traces remaining after the occurrence of changes in soul-life, and relating to those changes." Memory-images are included; but states of feeling, as such, are not presentations, though they become so through their results. While the common notion reduced all psychical phenomena to presentations, and yet named several 'chief psychical states,' Tetens rested his classification of faculties on no distinction of important states, but on the double power of the soul, receptivity and spontaneous activity. Instead of thinking and representing, he put forward willing and knowing as the forms of spontaneity, knowledge including both thought and representation. He neglected Wolfs doctrine of after-images, and substituted conclusions of his own, which anticipate the result of recent physiologists. His work is characterized by careful observation and research instead of by verbal subtleties; and when he did not differ from current conceptions, he rendered them more exact and significant. With the
