Substance (Lat. substare, substantia), the first of Aristotle's categories, signifies being as existing in and by itself, and serving as a subject or basis for accidents and accidental changes.
I.—Substance, being a genus supremum, cannot strictly be defined by an analysis into genus and specific difference; yet a survey of the universe at large will enable us to form without difficulty an accurate idea of substance. Nothing is more evident than that things change. It is impossible for anything to be twice in absolutely the same state; on the other hand all the changes are not equally profound. Some appear to be purely external: a piece of wood may be hot or cold, lying flat or upright, yet it is still wood; but if it be completely burnt so as to be transformed into ashes and gases, it is no longer wood; the specific, radical characteristics by which we describe wood have totally disappeared. Thus there are two kinds of changes: one affects the radical characteristics of things, and consequently determines the existence or non-existence of these things; the other in no way destroys these characteristics, and so, while modifying the thing, does not affect it fundamentally. It is necessary, therefore, to recognize in each thing certain secondary realities (see Accident) and also a permanent fundamentum which continues to exist notwithstanding the superficial changes, which serves as a basis or support for the secondary realities what, in a word, we term the substance. Its fundamental characteristic is to be in itself and by itself, and not in another subject as accidents are.
The Scholastics, who accepted Aristotle's definition, also distinguished primary substance (substantia prima) from secondary substance (substantia secunda): the former is the individual thing—substance properly so called; the latter designates the universal essence or nature as contained in genus and species. And, again, substance is either complete, e.g. man, or incomplete, e.g. the soul, which, though possessing existence in itself, is united with the body to form the specifically complete human being. The principal division, however, is that between material substance (all corporeal things) and spiritual substance, i.e. the soul and the angelic spirits. The latter are often called substantiae separatae, to signify that they are separate from matter, i.e. neither actually conjoined with a material organism nor requiring such union as the natural complement of their being (St. Thomas, "Contra Gentes", II, 91 sqq.). St. Thomas further teaches that the name substance cannot properly be applied to God, not only because He is not the subject of any accidents, but also because in Him essence and existence are identical, and consequently He is not included in any genus whatever. For the same reason, it is impossible that God should be the formal being of all things (esse formale omnium), or, in other words, that one and the same existence should be common to Him and them (op. cit., I, 25, 26).
In the visible world there is a multitude of substances numerically distinct. Each, moreover, has a specific nature which determines the mode of its activity and at the same time, through its activity, becomes, in some degree, manifest to us. Our thinking does not constitute the substance; this exists independently of us, and our thought at most acquires a knowledge of each substance by considering its manifestations. In this way we come to know both the nature of material things and the nature of the spiritual substance within us, i.e. the soul. In both cases our knowledge may be imperfect, but we are not thereby justified in concluding that only the superficial appearances or phenomena are accessible to us, and that the inner substantial being, of matter or of mind, is unknowable.
Since the close of the Scholastic period, the idea of substance and the doctrines centring about it have undergone profound modifications which in turn have led to a complete reversal of the Scholastic teaching on vital questions in philosophy. Apart from the traditional concept formulated above, we must note especially Descartes' definition that substance is "a being that so exists as to require nothing else for its existence". This formula is unfortunate: it is false, for the idea of substance determines an essence which, if it exists, has its own existence not borrowed from an ulterior basis, and which is not a modification of some being that supports it. But this idea in no way determines either the manner in which actual existence has been given to this essence or the way in which it is preserved. The Cartesian definition, moreover, is dangerous; for it suggests that substance admits of no efficient cause, but exists in virtue of its own essence. Thus Spinoza, following in the footsteps of Descartes, declared that "substance is that which is conceived in itself and by itself", and thence deduced his pantheistic system according to which there is but one substance—i.e. God—all things else being only the modes or attributes of the Divine substance (see Pantheism). Leibniz's definition is also worthy of note. He considers substance as "a being gifted with the power of action". Substance certainly can act, since action follows being, and substance is being par excellence. But this property does not go to the basis of reality. In every finite substance the power to act is distinct from the substantial essence; it is but a property of substance which can be defined only by its mode of existence.
II.—The most important question concerning substance is that of its reality. In ancient days Heraclitus, in modern times Hume, Locke, Mill, and Taine, and in our day Wundt, Mach, Paulsen, Ostwald, Ribot, Jodi, Hoffding, Eisler, and several others deny the reality of substance and consider the existence of substance as an illusory postulate of naive minds. The basis of this radical negation is an erroneous idea of substance and accident. They hold that, apart from the accidents, substance is nothing, a being without qualities, operations, or end. This is quite erroneous. The accidents cannot be separated thus from the substance; they have their being only in the substance; they are not the substance, but are by their very nature modifications of the substance. The operations which these writers would thus attribute to the accidents are really the operations of the substance, which exercises them through the accidents. Finally, in attributing an independent existence to the accidents, they simply transform them into substance, thus establishing just what they intend to deny. It can be said that whatever exists is either a substance or in a substance.
The tendency of modern philosophy has been to regard substance simply as an idea which the mind indeed is constrained to form, but which either does not exist objectively or, if it does so exist, cannot be known. According to Locke (Essay ii, 23), "Not imagining how simple ideas can subsist by themselves, we accustom ourselves to suppose some substratum wherein they do subsist and from which they do result; which therefore we call substance; so that if any one will examine himself concerning his notion of pure substance in general, he will find he has no other idea of it at all, but only a supposition of he knows not what support of such qualities, which are capable of producing simple ideas in us; which qualities are commonly called accidents." He protests, however, that this statement refers only to the idea of substance, not to its being; and he claims that "we have as clear a notion of the substance of spirit as we have of body" (ibid.). Hume held that the idea of substance "is nothing but a collection of simple ideas that are united by the imagination and have a particular name assigned to them, by which we are able to recall, either to ourselves or others, that collection" (Treatise, bk. I, pt. IV); and that the soul is "a bundle of conceptions in a perpetual flux and movement".
For Kant substance is a category of thought which applies only to phenomena, i.e. it is the idea of something that persists amid all changes. The substantiality and immortality of the soul cannot be proved by the pure reason, but are postulated by the moral law which pertains to the practical reason. J. S. Mill, after stating that "we may make propositions also respecting those hidden causes of phenomena which are named substances and attributes", goes on to say: "No assertion can be made, at least with a meaning, concerning those unknown and unknowable entities, except in virtue of the phenomena by which alone they manifest themselves to our faculties" (Logic, bk. i, I, c. v): in other words, substance manifests itself through phenomena and yet is unknowable. Mill defines matter as "a permanent possibility of sensation", so that no substantial bond is required for material objects; but for conscious states a tie is needed in which there is something "real as the sensations themselves and not a mere product of the laws of thought" ("Examination", c. xi; cf. Appendix). Wundt, on the contrary, declares that the idea (hypothetical) of substance is necessary to connect the phenomena presented in outer experience, but that it is not applicable to our inner experience except for the psycho-physical processes (Logik, I, 484 sqq.). This is the basis of Actualism, which reduces the soul to a series of conscious states. Herbert Spencer's view is thus expressed: "Existence means nothing more than persistence; and hence, in mind, that which persists in spite of all changes, and maintains the unity of the aggregate in defiance of all attempts to divide it, is that of which existence in the full sense of the word must be predicated—that which we must postulate as the substance of mind in contradistinction to the varying forms it assumes. But, if so, the impossibility of knowing the substance of mind is manifest" (Princ. of Psychol., Pt. II, c. i). Elsewhere he declares that it is the same Unknowable Power which manifests itself alike in the physical world and in consciousness—a statement wherein modern Agnosticism returns to the Pantheism of Spinoza.
This development of the concept of substance is instructive; it shows to what extremes subjectivism leads, and what inconsistencies it brings into the investigation of the most important problems of philosophy. While the inquiry has been pursued in the name of criticism, its results, so far as the soul is concerned, are distinctly in favor of Materialism; and while the aim was supposed to be a surer knowledge on a firmer basis, the outcome is Agnosticism either open or disguised. It is perhaps as a reaction against such confusion in the field of metaphysics that an attempt has recently been made by representatives of physical science to reconstruct the idea of substance by making it equivalent to "energy". The attempt so far has led to the conclusion that energy is the most universal substance and the most universal accident (Ostwald, "Vorlesungen uber Naturphilosophie", 2nd ed., Leipzig, 1902, p. 146).
For the theological significance of substance see Eucharist. See also Accident; Soul; Spiritualism.
M. P. DE MUNNYNCK