MECHANISM, or the MECHANICAL THEORY, in its most general significance. means the relation of a limited number of in variable substances to each other in such a way that they vary in their relations according to invariable laws. More specifically it means the explanation of phenomena by the universal laws of matter in motion. It is closely connected with the attempt to resolve bodies into their simplest elements and to explain their qualities as due to uniform laws of connection and inter action among these elements. The mechanical theory has usually been held in connection with some form of atomism. Since the aim of this kind of explanation is to reduce qualita tive determinations to quantitative and me chanical relations of elements, these elements have usually been conceived to possess only such 9ualities as were necessary to explain the empirical qualities, the ideal being to find a single homogeneous element possessing only the characteristics essential to corporeity_ The term mechanical is also used in a looser sense, though still within the limits of the general definition given above, to describe any explana tion which regards all the qualities of a body as due to the mere summation of the qualities of its parts; e.g., a mechanical theory of Mechanism as a Theory of the World.— As a philosophical theory, mechanism is the at tempt to regard the entire universe as a closed system of causes and effects in which every change is ultimately reducible to a change of motion. In this sense, therefore, it is prac tically synonymous with materialism (q.v.).
Mechanism as a Method of Explanation. —After the Middle Ages the development of the new science, at the hands of Copernicus, Kepler and Galileo (qq.v.), and many of their contemporaries, depended very largely on the application to nature of the method of mechan ical explanation. Francis Bacon (1561-16-15) (q.v.), by his opposition to the use of teleology in scientific explanation, did much to bring about the acceptance of mechanism, and it was firmly established as the true scientific method of dealing with nature by Descartes (15% 1650) (q.v.), who, though not an atomist, still denied to matter all but quantitative character istics and defined the method of science as strictly mechanical. Even the physical phe nomena of living bodies (everything in the world, in fact, except the res cognans in man) he regarded as capable of a purely mechanical explanation. From this time on mechanism be came the recognized method for natural science, and consequently it soon became an urgent philosophical problem to discover a satisfactory way of reconciling the mechanical conception of nature with a teleological and idealistic con ception of the universe. Thus Leibniz (16>6 1716) (q.v.), while admitting the necessity of reducing all natural phenomena to motion, held that ultimate reality consists of an infinity of centres of force (monads), which he conceives as in some sense analogous to minds. Accord ingly, metaphysical explanation must be in, terms of teleology, though mechanism is the sole valid explanation of the phenomenal mani festation of reality in nature. A similar con ception, having its historical origin in Leibruz, was held in the 19th century by Lotze (1817 81) (q.v.), who proclaims the purpose of his philqsophy to be "to show how absolutely uni versal is the range of mechanism, and at the same time how completely subordinate the significance of the function which it has to ful fil in the structure of the world" mus,' Introduction). Kant also regards the mechanical categories as the sole valid means of scientific explanation. The causal category is, for him, rigorously constitutive of our ex perience and hence is determinant of our con ception of all objects in the world of experi ence; teleology, on the other hand, though. a necessary means of regulating our investiga tions of organized matter, remains a merely subjective principle which can give no insight into the origin of any being. When we deal with objects which "cannot be thought by us, as regards their possibility, according to the principle of mechanism," we may treat them "as if" they were teleologically ordered; but "nothing is gained for the theory of nature or the mechanical explanation of its phenomena by means of its effective causes, by considering them as connected according to the relation of purposes." The phenomena of the moral life,
according to Kant, lie outside the realm of sci entific experience and hence are not subject to mechanical explanation. Since Kant's time, many thinkers, perhaps the majority, have fol lowed him in regarding mechanism as the ulti mate principle of explanation for science; thus Helmholtz, F. A. Lange, Dubois-ReYmond, Clausius, Thomson, Maxwell, etc. Wundt at tempts to find for it a logical justification as the only theory which can afford an adequate conception of natural causality. On the other hand, more recent writers, especially among physicists, have taken the opposite view. Ac cording to them, the pre-eminence of mechan ical explanation is merely a dogma based on its successful use in science. E. Mach, Stallo, Helm and H. Cornelius take this position. These thinkers maintain that the purpose of scientific explanation is to condense into a single compact statement (e.g., a mathematical formula) a large mass of empirical data. A scientific law is merely a short-hand statement of the facts, and its value is purely economic. So long as the mechanical theory affords useful analogues for the formulation of other phe nomena, it is a valid scientific method. When ever this ceases to be the case, mechanism must be superseded by a more economical theory. Kant's conception of mechanism as a mode of dealing with experience has been developed by contemporary English idealism. The general problem of all rational knowledge is conceived to be the construction and maintenance of a coherent and systematic experience. In all thought, therefore, there is implied a totality which constitutes the truth. But this totality manifests itself in different categories of thought and in varying degrees of perfection. "Matter and motion are the abstractions in which the sensuous world is reduced to homo geneity in order to be susceptible of quantita tive treatment, and in this treatment they are able to a large extent to represent genuine and actual relations of that world' (Bosanquet, Vol. I,. p. 200). Mechanical explana tion, therefore, is one form in which the unity of thought may be manifested; it is "that form of identity and difference in which an identity is regarded as the sum of the difference in which it is presented" (ib., p. 201). Its value for knowledge is therefore said to be instru mental or methodological, because it is a method which thought uses in its effort to con struct a rational experience. It possesses ulti mate truth just in proportion to the degree of rational unity it achieves in experience as a whole.
In psychology the term mechanism is some times used to describe a theory which seeks to explain mental phenomena as due to the com bination or interaction of simply psychic ele ments. This usage is an analogy with the atomic theory of matter. The classical example is Herbart (q.v.), who gave the term currency. According to his theory every representation has a constant quality and a variable force. These forces stand in relations of greater or less opposition and the whole state of con sciousness is conceived as a resultant of all the forces involved in it. Consult Th. Ribot's Psychology of To-day' (Eng. trans. by M. Baldwin, pp. 24 ff.). For mechanism in biology see MECHANISM AND VITALISM.
Bibliography.—Lange, F. A., (History of Materialism' (Eng. trans., London 1879-81, 3 vols.) ; Kurt, Lasswitz, (Geschichte der Atomis tik vom Mittelalter bis Newton> (Hamburg 1890, 2 vols.) • Lotze, (Metaphysic,' Book II (Eng. trans., Oxford 1:;7, 2 vols.); Sigwart, C., (Logic, § 100 (Eng. trans., London 1895, 2 vols.); Ward, James, (Naturalism and Ag nosticism,' Part I (2d ed., London 1903, 2 vols.); Mach, E., Scientific Lectures' (Eng. trans., Chicago 1895).