%1. Natural Philosophy and Psychology.%
In Locke's famous countryman, Isaac Newton (1642-1727),[1] the modern investigation of nature attains the level toward which it had striven, at first by wishes and demands, gradually, also, in knowledge and achievement, since the end of the mediaeval period. Mankind was not able to discard at a stroke its accustomed Aristotelian view of nature, which animated things with inner, spirit-like forces. A full century intervened between Telesius and Newton, the concept of natural law requiring so long a time to break out of its shell. A tremendous revolution in opinion had to be effected before Newton could calmly promulgate his great principle, "Abandon substantial forms and occult qualities and reduce natural phenomena to mathematical laws," before he could crown the discoveries of Galileo and Kepler with his own. For this successful union of Bacon's experimental induction with the mathematical deduction of Descartes, this combination of the analytic and the synthetic methods, which was shown in the demand for, and the establishment of, mathematically formulated natural laws, presupposes that nature is deprived of all inner life [2] and all qualitative distinctions, that all that exists is compounded of uniformly acting parts, and that all that takes place is conceived as motion. With this Hobbes's programme of a mechanical science of nature is fulfilled. The heavens and the earth are made subject to the same law of gravitation. How far Newton himself adhered to the narrow meaning of mechanism (motion from pressure and impulse), is evident from the fact that, though he is often honored as the creator of the dynamical view of nature, he rejected actio in distans as absurd, and deemed it indispensable to assume some "cause" of gravity (consisting, probably, in the impact of imponderable material particles). It was his disciples who first ventured to proclaim gravity as the universal force of matter, as the "primary quality of all bodies" (so Roger Cotes in the preface to the second edition of the Principia, 1713).
[Footnote 1: 1669-95 professor of mathematics in Cambridge, later resident in London; 1672, member, and, 1703, president of the Royal Society. Chief work, Philosophic Naturalis Principia Mathematica, 1687. Works, 1779 seq. On Newton cf. K. Snell, 1843; Durdik, Leibniz und Newton, 1869; Lange, History of Materialism, vol. i. p. 306 seq.]
[Footnote 2: That the mathematical view of nature, since it leaves room for quantitative distinctions alone, is equivalent to an examination of nature had been clearly recognized by Poiret. As he significantly remarked: The principles of the Cartesian physics relate merely to the "cadaver" of nature (Erud., p. 260).]
Newton resembles Boyle in uniting profound piety with the rigor of scientific thought. He finds the most certain proof for the existence of an intelligent creator in the wonderful arrangement of the world-machine, which does not need after-adjustment at the hands of its creator, and whose adaptation he praises as enthusiastically as he unconditionally rejects the mingling of teleological considerations in the explanation of physical phenomena. By this "physico-theological" argument he furnishes a welcome support to deism. While the finite mind perceives in the sensorium of the brain the images of objects which come to it from the senses, God has all things in himself, is immediately present in all, and cognizes them without sense-organs, the expanse of the universe forming his sensorium.
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The transfer of mechanical views to psychical phenomena was also accompanied by the conviction that no danger to faith in God would result therefrom, but rather that it would aid in its support. The chief representatives of this movement, which followed the example of Gay, were the physician, David Hartley[1] (1704-57), and his pupil, Joseph Priestley,[2] a dissenting minister and natural scientist (born 1733, died in Philadelphia 1804; the discoverer of oxygen gas, 1774).
The fundamental position of these psychologists is expressed in two principles: (1) all cognitive and motive life is based on the mechanism of psychical elements, the highest and most complex inner phenomena (thoughts, feelings, volitions) are produced by the combination of simple ideas, that is, they arise through the "association of ideas "; (2) all inner phenomena, the complex as well as the simple, are accompanied by, or rather depend on, more or less complicated physical phenomena, viz., nervous processes and brain vibrations. Although Hartley and Priestley are agreed in their demand for an associational and physiological treatment of psychology, and in the attempt to give one, they differ in this, that Hartley cautiously speaks only of a parallelism, a correspondence between mental and cerebral processes, and rejects the materialistic interpretation of inner phenomena, pointing out that the heterogeneity of motion and ideas forbids the reduction of the latter to the former, and that psychological analysis never reaches corporeal but only psychical elements. Moreover, it is only with reluctance that, conscious of the critical character of the conclusion, he admits the dependence of brain vibrations on the mechanical laws of the material world and the thoroughgoing determinateness of the human will, consoling himself with the belief that moral responsibility nevertheless remains intact. Priestley, on the contrary, boldly avows the materialistic and deterministic consequences of his position, holds that psychical phenomena are not merely accompanied by material motions but consist in them (thought is a function of the brain), and makes psychology, as the physics of the nerves, a part of physiology. The denial of immortality and the divine origin of the world is, however, by no means to follow from materialism. Priestley not only combated the atheism of Holbach, but also entered the deistic ranks with works of his own on Natural Religion and the Corruptions of Christianity.
[Footnote 1: Hartley, Observations on Man, his Frame, his Duties, his
Expectations. 1749.]
[Footnote 2: Priestley, Hartley's Theory of the Human Mind on the Principles of the Association of Ideas, 1775; Disquisitions relating to Matter and Spirit, 1777; The Doctrine of Philosophical Necessity, 1777; Free Discussions of the Doctrines of Materialism, 1778 (against Richard Price's Letters on Materialism and Philosophical Necessity). Cf. on both Schoenlank's dissertation, Hartley und Priestley, die Begründer des Assoziationismus in England, 1882.]