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.

* * * * *

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.