6.2 History of substance

To clarify the content and consequences of the new ideas about substances given in the previous two chapters, we examine a short list of historical comparisons and contrasts.

The Pythagoreans held that the principles of mathematics are the principles of all things. In other words, the basic structure of Being is mathematical. We find it difficult to understand how a mathematical object (a form) could constitute the entirety of a physical object that is concrete and changeable. The Pythagoreans had not taken into account the powers of objects, and they therefore lacked a concept of concrete underlying substance.

Aristotle used the name hyle (matter) for the underlying stuff of which objects are formed, in the way that a statue is formed of clay. He recognized that the resulting objects had potentialities for changing themselves or others, but unfortunately he attributed that ability to added form rather than to substance.

This neglect of underlying powers became more critical in Thomism, when hyle (matter) was reduced to only ‘pure potency’: that which is only capable of receiving forms. Non-trivial or active powers or dispositions were not attributed to matter, but only to the added forms. This mistake has long persisted and is only now, with the revival of interest in dispositions and powers, being remedied. Today the underlying matter or substance is recognized for its more active role in nature. We insist that mere forms, qua form, have themselves no active powers or dispositions. Indeed, they can never exist by themselves in nature.

A different philosophical idea of substance was held by Spinoza and Leibniz. They defined substance as ‘that whose nature requires its separate existence’. In this view, substances are self-sufficient beings that contain within themselves the complete source of all their changes. Leibniz claimed that all natural changes of his monads come from within, as “an external cause can have no influence upon its inner being” (Leibniz, 1714, para. 11). The difficulty then, as Kant realized, is that on this account “it is not necessary for [a substance’s] existence that it stand in relation to other things” (Kant, 1747, Section 7). It is then puzzling that substances have positional relations, such as those which enable the acting of one substance on another. The possibility of interactions of substances can only be regained by denying that substances are self-sufficient beings. They persist, not autonomously, but for interactions.

Descartes is famous for his dualism of two substances: the mental that is essentially rational and the material that is essentially extension. In this view of nature as that which is extended, extensiveness is a geometrical form. Descartes is known in mathematics for his new coordinate analyses of geometry. But something is missing, we now realize. There is no component of power and hence no idea of natural substance.

Boyle, Locke and Newton, in contrast, had both the necessary ingredients. Their ‘solid corpuscular substances’ had both form (spherical or other shapes) and powers (hardness, impenetrability, mobility, and inertia of parts, according to Bk. III of Newton’s Principia). This union of form and power enabled complete explanations in the sense of Section 4.5 above. Their explanations were logically coherent by my proposal. However, Newton’s postulated existence of universal gravity, with its action at a distance, was still puzzling. Did the corpuscles have power at distances where they had no substance? That seemed to violate some principle, but which? I say that it is because we have an intuitive understanding of the deep connection between power and substance that we are uneasy when objects have powers at a distance, namely where their substance is not.

These difficulties became more severe with the further discoveries of magnetism, electric fields and (astonishingly) propagating electromagnetic waves. Boscovich wanted to accept that substances had powers extended away from a mass point in space, but Faraday argued that these fields were real in their own way--just as real as atoms. They must have some kind of ‘substance’ of their own since they have persisting powers. This is just as I now argue in general.

The puzzle about the substantiality of electromagnetic fields is resolved in modern physics. According to quantum field theory, these fields are composed of propagating photons. These photons carry momentum and energy, so, according to the relativistic E=mc², they have gravitational mass as well. There can be no objection to identifying them as substances. The only problem is the probabilistic nature of virtual photons and their quantum behavior, as discussed in Subsection 5.3.1. Other fields (nuclear and gravitational) are posited to be composed of their own field quantum particles (gluons and gravitons, respectively).

The philosophical implications of modern physics are still being assimilated. At the start of the twentieth century there was a denial of ‘substance’ altogether and of any sense of continued identity, in favor of pure process. They had a purely event or flux philosophy. Reasons for this repudiation varied. Sometimes it was the alleged unknowability of the real constitution of substances. At other times it was a preference for ‘flux’ or ‘creativity’ as against the ‘Parmenidean influence’ that was seen to pervade much of Western philosophy. Hume and Whitehead were the two most prominent influences here. Between the World Wars last century, an ontology of ‘events’ became popular, especially with the influence of a common interpretation of relativity theory and a positivistic approach to metaphysics. Russell’s The Analysis of Matter (1927) was a good presentation of this position, wherein events are fixed in space and time. Paradoxically, they then became like fixed substances, and the understanding of event as change faded.

After the Second World War, Rescher (1962) noted that there was a general reaction to such an extreme event-and-no-continuant ontology, and many writers repudiated ‘events’ in favor of substances and their relations. A very uncritical idea of ‘substance’ was accepted, practically identical with ‘material object’. This had the result that there could be no very precise understanding of either the fact or the dynamics of real change. Recent work on powers and dispositions is on the way to remedying these failures. The program of dispositional essentialism should take its next step and discover how it can reconstitute a good account of substance based on dispositions.