This definition of substantial compound is very different from that which the scholastics drew from their theory of substantial generations. But since chemistry has shown, and philosophical reasoning based on facts confirms, that what in such a theory is called the “generated substance” is only a compound of substances, it must be evident that our substantial compound, as above defined, does not, in fact, differ from theirs, but is the same thing viewed under a different light. Perhaps, if the schoolmen had thought that bodies were possibly but the result of the composition of many permanent substances, they would not have called them _substantial_, but only _natural_, compounds; yet, since the epithet “substantial” has been originally adopted, and is still commonly applied to compounds which we know actually to contain many distinct substances, we cannot keep the word “substantial” without giving it such a meaning as will answer to the real nature of the things it qualifies. Nevertheless, should the reader prefer to apply the epithet “substantial” to that compound only which consists of matter and substantial form interpreted in accordance with the Peripatetic system, then the compounds of which we treat might be called _natural_, or _essential_, compounds, or _compound natures_. So long, however, as such compounds are called “substances,” we think we have the right to apply to them the epithet “substantial.” The immediate principles of substantial compound are three, as in the primitive being: to wit, _act_, _term_, and _complement_; but they are of a different nature, as we are going to explain. Two cases are to be examined. For the physical parts, which unite to make one compound nature, sometimes rank all alike as material constituents of the compound, as in water, iron, silver, and other natural bodies; but at other times one of the constituent substances stands forth in the character of a form, as the human soul in the body, all the parts of the body remaining under it, and making up the complete material constituent of the compound nature. In the first case, the physical components taken together constitute the adequate _potential term_ or the compound nature; because, as they are all alike material constituents, they are all alike potential respecting their composition; and thus they are all equally liable to be tied together by physical action. The specific composition will be the _act_ of the compound essence; for it is such a composition that formally binds together those physical components into one specific compound. Finally, the actual bond of the components, brought about by their composition, will be the actuality of the compound nature—that is, its formal _complement_.