INDEX

Introduction to the Philosophy of St. Thomas Aquinas

Ch 2: The Principles of Mobile Being

IV. The Structure of Corporeal Substances (cont)

b) Mixtures. - Besides elements nature affords what Aristotle calls "mixtures," amalgams of several elementary substances, i.e., elements. These complex bodies are unified wholes with specific properties that differ from the properties of individual elements. Aristotle's principal discussion of such bodies occurs in De Generatione et Corruptione, where his main purpose is to show that they originate by a process that appears to fall short of outright generation, yet is more than a juxtaposing of pre-existent elements.

Two conclusions emerge from his analysis. First, a mixture is a real fusion of substantial elements, giving rise to a new substance unified under a single substantial form. Secondly, in a mixture the elements survive, but in a "virtual" state, which means they retain a measure of their individual activity and hence of their individual qualities.

In his Commentary St. Thomas recapitulates the notion of mixture as follows: "For there to be a mixture the miscible bodies must be neither completely corrupted nor completely the same as before; therefore, they are corrupted as to form, but remain as to operative power." 22

Mixtures, then, are more than aggregates; they are true substances. To say they are substances implies they have but one substantial form and originate by substantial generation. What is peculiar to them is that the component elements, instead of being reduced to utter potency, maintain a manner of persistence not found when a substance is completely corrupted, and this survival expresses itself on the plane of activity.23

Aristotle's theory of mixtures served him on two counts. It gave him an explanation for the survival, such as it is, of the elements in certain complex substances; and it enabled him to reject the atomistic solution, which regarded mixtures simply as juxtapositions of pre-existent bodies. But though the theory served Aristotle, does it still avail? Its scientific perspective belongs, no doubt, to the past and may be disregarded, but basically the theory seems to stand. Until now, at any rate, there has been no indication that the philosophical analysis, say of the modern molecule or chemical compound, can go much beyond the point Aristotle reached in his analysis of mixtures.

Footnotes

22 "Ad hoc quod sit mixtio necesse est quod miscibilia nec sint simpliciter corrupta, nec sint simpliciter eadem ut prius: sunt enim corrupta quantum ad formas, et remanent quantum ad virtutem" (In I De Generat., lect. 25, no. 12).

23 Neither Aristotle nor St. Thomas means to suggest, however, a third kind of change in addition to accidental and substantial change. What they are saying is that some complex bodies continue to display the properties which their component elements displayed separately. Nor are they implying that for an element there is a third kind of existence, neither actual nor potential but in between. And when they say that sometimes the elements remain quantum ad virtutem, as to their operative power, they do not mean that the property of a thing can exist without the thing's substantial form. If a mixture exhibits the same, or some of the same properties found in the elements individually, these properties now spring from the one substantial form of the mixture, and not from the vanished forms of the elements that went into the mixture. Consulted with profit on the notion of mixtures may be Christian L. Bonnet, "Note on the Thomistic Interpretation of Complex Individual Bodies," The Modern Schoolman, XXI, 2 (1944), 101-107; idem, "The Unity of the Complex Individual Body," ibid., XXII, i (1944), 33-43. - Translator's note.

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