sterhuis (1721-90; _Works_, new ed., 1846-50), and the
philologists Wyttenbach and Van Heusde. Then Cornelius Wilhelm Opzoomer[3]
(1821-92; professor in Utrecht) brought in a new movement. Opzoomer
favors empiricism. He starts from Mill and Comte, but goes beyond them in
important points, and assigns faith a field of its own beside knowledge.
In opposition to apriorism he seeks to show that experience is capable of
yielding universal and necessary truths; that space, time, and causality
are received along with the content of thought; that mathematics itself is
based upon experience; and that the method of natural science, especially
deduction, must be applied to the mental sciences. The philosophy of mind
considers man as an individual being, in his connection with others, in
relation to a higher being, and in his development; accordingly it
divides into psychology (which includes logic, aesthetics, and ethology),
sociology, the philosophy of religion, and the philosophy of history.
Central to Opzoomer's system is his doctrine of the five sources of
knowledge: Sensation, the feeling of pleasure and pain, aesthetic, moral,
and religious 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
defective 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 we 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).

[Footnote 1: Opzoomer: _The Method of Science_, a Handbook of Logic, German
translation by Schwindt, 1852; _Religion_, German translati