criminated by Descartes and Hobbes. The same conception (motion) is used to explain the feelings, which, when pleasurable, are the result of the vital motion being "helped" by the motions which, having produced conceptions in the head, afterward proceed to the heart.[1] But external objects not only "cause conceptions, and conceptions appetite, and fear;" as the latter are "the first unperceived beginnings of our actions," and as in a state of doubt, appetite and fear rapidly succeed one another, "this alternate succession of appetite and fear.... is that we call deliberation."[2] As all Hobbes's successors of the same school have followed him in thus ignoring the ego, it may be inferred that every system of experimental psychology is self-condemned to incompleteness, and that no system can cover the whole of the ground which does not make what can only be called metaphysical assumptions.
The psychological advances made by Hobbes were then—that he helped to banish the imaginary entities of the Schoolmen, and substituted for them hypotheses that implied at least veræ causæ (true causes); that he replaced the method of deduction from assumed principles by that of observation (which was not yet, however, that of introspection), and thus founded the inductive philosophy of the mind; and that by his summary rejection of the common metaphysical assumptions, and his patient building up on an independent foundation, he decisively separated psychology from the metaphysics in which it was enmeshed.
If the psychology of Hobbes bears evident marks of the daring, speculative character of contemporary physical science, that of Locke witnesses to the change in the tone and spirit of inquiry. If the keyword to Hobbes is Galileo, that to Locke is Sydenham. Locke and Sydenham were both surgeons, were friends, and were of kindred cautious temperament; and the pacific revolution which Sydenham wrought in medicine has been described in language that, with the necessary change of terms, might word for word be applied to the great psychological advance initiated by Locke. A competent writer describes Sydenham as being—
"most careful to exclude the prevailing theories from affecting his study of the facts of disease: he followed the inductive method which his countryman, Bacon, had just completed, and under the guidance of his friend John Locke, himself a surgeon, he applied it to the investigation of disease with splendid success. The laws ruling the prevalence of epidemics were elucidated, and new and old diseases described with an accuracy and graphic coloring which have ever since remained unrivaled. The treatment of disease Sydenham found lamentably uncertain from want of any fixed principle, and from the countless remedies prescribed mainly in accordance with a capricious fashion. In place of this, he left therapeutics an art ordered by the principle of aiding Nature, and observing the indications afforded by morbid processes themselves....
