Discourse on Metaphysics and the Monadology. Gottfried Leibniz

      Introduction

      BY PAUL JANET

      When Descartes, in the first half of the seventeenth century, said that there are only two kinds of things or substances in nature, namely, extended substances and thinking substances, or bodies and spirits; that, in bodies, everything is reducible to extension with its modifications of form, divisibility, rest and motion, while in the soul everything is reducible to thinking with its various modes of pleasure, pain, affirmation, reasoning, will, etc. . . . ; when he in fact reduced all nature to a vast mechanism, outside of which there is nothing but the soul which manifests to itself its existence and its independence through the consciousness of its thinking, he brought about the most important revolution in modern philosophy. To understand its significance however, an account must be given of the philosophical standpoint of the time.

      In all the schools at that time the dominant theory was that of the Peripatetics, altered by time and misunderstood, the theory of substantial forms. It posited in each kind of substance a special entity which constituted the reality and the specific difference of that substance independently of the relation of its parts. For example, according to a Peripatetic of the time, “fire differs from water not only through the position of its parts but through an entity which belongs to it quite distinct from the materials. When a body changes its condition, there is no change in the parts, but one form is supplanted by another.”{1} Thus, when water becomes ice, the Peripatetics claimed that a new form substituted itself in place of the preceding form to constitute a new body. Not only did they admit primary or basal entities, or substantial forms to explain the differences in substances, but for small changes also, and for all the sensible qualities they had what were called accidental forms: thus hardness, heat, light were beings quite different from the bodies in which they were found.

      To avoid the difficulties inherent in this theory, the Schoolmen were led to adopt infinite divisions among the substantial forms. In this way the Jesuits of Coimbre admitted three kinds of these forms: first, the being which does not receive its existence from a superior being and is not received into an inferior subject,—this being is God; second, the forces which receive their being from elsewhere without being themselves received into matter,—these are the forms which are entirely free from any corporeal concretion; third, the forms dependent in every respect, which obtain their being from a superior cause and are received into a subject,—these are the accidents and the substantial forms which determine matter.

      Other schoolmen adopted divisions still more minute and distinguished six classes of substantial forms, as follows: first, the forms of primary matter or of the elements; second, those of inferior compounds, like stones; third, those of higher compounds, like drugs; fourth, those of living beings, like plants; fifth, those of sensible beings, like animals; sixth, above all the rest, the reasoning (rationalis) substantial form which is like the others in so far as it is the form of a body but which does not derive from the body its special function of thinking.

      Some have thought, perhaps, that Molière, Nicole, Malebranche and all those who in the seventeenth century ridiculed the substantial forms, calumniated the Peripatetic Schoolmen and gratuitously imputed absurdities to them. But they should read the following explanation, given by Toletus, of the production of fire: “The substantial form of fire,” says Toletus, “is an active principle by which fire with heat for an instrument produces fire.” Is not this explanation even more absurd than the virtus dormitiva? The author goes on to raise an objection, that fire does not always come from fire. To explain this he proceeds, “I reply that there is the greatest difference between the accidental and the substantial forms. The accidental forms have not only a repugnance but a definite repugnance, as between white and black, while between substantial forms there is a certain repugnance but it is not definite, because the substantial form repels equally all things. Therefore it follows that white which is an accidental form results only from white and not from black, while fire can result from all the substantial forms capable of producing it in air, in water or in any other thing.”

      The theory of substantial or accidental forms did more than to lead to nonsense like the above; it introduced errors which stood in the way of any clear investigation of real causes. For example, since some bodies fell toward the earth while others rose in the air, it was said that gravity was the substantial form of the former and lightness of the latter. Thus heavy and light bodies were distinguished as two classes of bodies having properties essentially different, and they were kept from the inquiry whether these apparently different phenomena did not have an identical cause and could not be explained by the same law. It was thus again that seeing water rise in an empty tube, instead of inquiring under what more general fact this phenomena could be subserved, they imagined a virtue, an occult quality, a hatred on the part of the vacuum, and this not only concealed the ignorance under a word void of sense but it made science impossible because a metaphor was taken for an explanation.

      So great had become the abuse of the substantial forms, the occult qualities, the sympathetic virtues, etc., that it was a true deliverance when Gassendi on the one hand and Descartes on the other founded a new physics on the principle that there is nothing in the body which is not contained in the mere conception of bodies, namely extension. According to these new philosophers all the phenomena of bodies are only modifications of extension and should be explained by the properties inherent in extension, namely, form, position, and motion. Upon this principle nothing happens in bodies of which the understanding is not able to form a clear and distinct idea. Modern physics seems to have partially confirmed this theory, when it explains sound and light by movements (vibrations, undulations, oscillations, etc.), either of air or of ether.

      It has often been said that the march of modern science has been in the opposite direction from the Cartesian philosophy, in that the latter conceives of matter

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