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9.4 Questions about Substances     9.4.1 Individuals     Since an unchanging continuant has constant powers so long as it lasts, it is that respect similar to the `Parmenidean Individuals' of Harré [1970b]. According to Harré, `Parmenidean individuals' are the ultimate individuals in nature at whatever level of microscopic analysis that may turn out to be, so the scientist does not have recourse to the internal arrangement of its parts to explain the powers of such an individual. It used to be thought, for example, that atoms were Parmenidean individuals, then (later) protons and electrons. The most likely present-day candidates are quarks, leptons and field quanta such as gluons and photons. The arrangement of their parts is not needed, because they are the ultimate individuals, and their internal constitution is not separate from their powers. Since they have no separable constituents, their nature must be identical with the particular form of all their powers. That is, to completely specify the powers of a Parmenidean individual is to completely specify its nature, its real constitution, and vice versa. This is in contrast to what Harré calls an `Aristotelean individual', which is a complex individual whose powers are explained by means of the dispositions (i.e. powers and arrangements) of its parts. Harré's Parmenidean individuals, however, endure indefinitely, and ``cannot be altered, $\ldots$ being the bearers of numerical identity [they] cannot be transformed'', whereas the `continuants', as being conceived in the present inquiry, do not necessarily last indefinitely, only at least for a while.   The process derivation of `continuants' has the feature that in it we can see more clearly how the nature of a continuant (as a propensity field) can be identical with the `particular form of all its powers'. This is because, as was seen just above, all the powers of a propensity field are given by its `substantial form': the form of the field as an extensive distribution of propensity.   This is in broad agreement with Ducasse's [1964] account of how a substant is related to its capacities. He argues that contrary to what the etymology of `substant' may suggest, the relation between a substant and its capacities it `has' is not analogous to the relation between, for example, a table and the objects it `stands under' and `supports'. Rather, the relation between a substant and its capacities is analogous to that which obtains between, for instance $\ldots$ an automobile and its parts; or a living body and its organs; or more generally between any whole and its parts. Now, on the present account, a propensity field is a single whole particular thing, and has various possibilities for actualising contained within its extent because it extends and endures (by definition) over all the places possible. One can regard the relation between a propensity field and the places possible within it, or equivalently between a continuant and the interactions possible for it, as therefore just the relation between a unitary whole and the parts into which it may possibly (not actually!) be divided. One important consequence of this account of the continuant as a `whole' with respect to its powers as `parts' means that continuants cannot ever be properly conceived apart from their powers.     Thus there never exists any separable, pure or `naked' substance. The only qualification I would give to Ducasse's account is to note that the actings of a continuant are most often interactions with other continuants, so that an account of a continuant's powers -- what it is capable of doing and how it is capable of interacting -- must make some reference to the condition of the other continuants with which it reciprocally interacts, and not depend only upon its own substantial form.       9.4.2 Matter and Form: Subject and Predicate We are now in the position of being able to identify the matter and form of the continuants defined above. Since an `unchanging continuant' has been defined as a single potentiality field, the powers of that continuant, what it is capable of doing, must be completely given by the extensive form of that field.     This form for any continuant may therefore be called its substantial form, and for an unchanging continuant is again strictly unchanging. A continuant retains exactly the same powers as long as it lasts.     This substantial form can be regarded as a predicate qualifying `propensity-as-such', as it is propensity (as such) which has that form. Propensity, therefore, can be regarded as the underlying `substance' or `matter' of all enduring continuants, which are therefore `forms of propensity'. `Propensity' is thus the logical subject -- `that which is not predicated of something else' -- and the substantial form is a predicate qualifying this subject. Propensity is capable of being a subject or a substance, because propensities are kinds of potentialities, and because of the way we resolved the problem of change in chapter 7. There, we saw that in order for potentialities to produced actualities, they had to have some kind of being themselves. That is, potentialities had to exist as `things' just as much as actualities were assumed to do. The alternative to this position would have to have `potential objects' waiting in some kind of limbo before some of them changed to be fully actual. We rejected any kind of `subsistence' like this, and instead we hold that various kinds of potentialities themselves exist as things. That of which they are formed, namely the potentiality itself, is therefore the substance or logical subject of the existing thing.   Traditionally, following Aristotle, this underlying subject is called the matter out of which natural things are constituted. I will not be using this term, as today it leads too readily to the concept of `material substance' of Boyle, Locke and Newton. As I wish to have a concept of substance which is to some extent independent of classical physics, the term `matter' will be used as little as possible.     Knowability of Matter/Propensity and Form For Aristotle, form is that which gives structure to matter such that it can be known. Matter, for Aristotle as here, was potentiality for natural being, but for Aristotle, matter is ``that which in itself is neither a particular thing nor of a certain quantity nor assigned to any of the other categories by which being is determined.'' 9.6 Aristotle appears to be looking for a kind of substratum when all qualities and quantities are stripped away, and his followers have interpreted this as the quest for prime matter (see below). Even if we take Aristotle's definition of matter to be the matter of specific things, he makes it difficult for us to say anything positive about it. All the intelligibility -- everything that makes a substance knowable to us -- seems to reside in the form rather than in the matter. It is the qualities and quantities (which make up the form) that appear readily to the intellectual understanding, with the underlying matter or subject appearing only in a negative charactisation. We cannot know matter `in itself', he might argue, because it is form incorporating matter which is perceived by the senses, and it is pure form which is considered by the mind. There are somewhat similar problems in the philosophy of nature. Although we have characterised the substance or the `subject' of things as propensity, and have characterised propensity as the probabilistic potentiality for actuality (and for nothing else), it is still left uncertain what propensity is in itself. We certainly know the forms in which propensity appears, for these are the field structures of mathematics, but I have not said what it is. The best answer to this is that we must content ourselves with knowledge of everything that a propensity does, and then to take a propensity as the minimal `that which is necessary to do all these things'. Thus propensities, and the substances they form, are defined as the unity of all their powers of operation. There is no reference to anything hidden that might be there as well as this unity: all the substance is `up front' in the capacities for operations. We thus have a kind of operationalism, but with the modal `possibilities for operations' taken realistically. In any case, if substances are forms of propensities, when we observe substances it must be these propensities which we observe. Of course, we do not observe them as propensities in themselves: we only observe the propensities as they produce effects. It is not the case that we only perceive effects, as the effects are interaction events, and hence are our acts of perception, not the objects of our perception. The objects of our perception are the propensities at the moment when they produce effects. There must therefore be a sense whereby we can say that a propensity is `in' its effects, as during its effects, what we do observe is the substance constituted by that propensity.         Prime Matter? In the Thomist traditions, there is an ultimate subject defined as the `pure capacity to receive determination', and called `pure potency', `primary potency', or even `prime matter'. It is thus rather more abstract than `propensities for actuality', which are always propensities for specific events and are thus to some extent already determinate even if not localised in space or time. The Thomist concept of `pure potency' or `pure capacity to receive determination' takes only the `possibility' component of the logical analysis of section 7.2, and is therefore a somewhat limited abstraction. Perhaps it is even a self-contradictory one, for is not to call it `pure potency' to give it some determination? There have been doubts whether such a concept is intelligible, but fortunately it is not needed for the present enterprise. We need only the concept of `propensity' or `power', as we only want to have a concept of the logical subject or substance of particular things.       9.4.3 On Real Essences Since the `substantial form' of a continuant is that on which all its powers depend, it may be called the `real essence' of that continuant.   The `real essence' is defined by Locke as `the internal, but generally (in substances) unknown, constitution, whereon their discoverable qualities 9.7 depend'9.8. They may often have been unknown, but that does not mean that they are unknowable. I argue that the `real essences' of continuants, the `substantial forms' of continuants as propensity fields, are in principle quite knowable, especially as many fields can be very easily described mathematically.   As Copi [1954] has pointed out, `it must be admitted that the doctrine of the unknowability of real essences was not an unreasonable doctrine to draw from the relatively undeveloped state of science in Locke's day', drawing attention to Locke's description9.9 of the then sorry state of chemistry. It is, however, the real essences of things which science seeks to discover, and the sciences have made considerable progress since Locke's day. It should always be remembered that these `real essences' are always the real essences of particular things. While we can intellectually distinguish the idea of the essence or form of a particular from the idea of that particular thing, that does not mean that the essence or form actually exists apart from that particular object in the world. The real essence is present only so long as the object continues to exist.     They are not the `essences' of the medieval neo-Aristoteleanism heavily tinged with neo-Platonism, of which a certain number were supposed, `according to which all natural things are made and wherein they do exactly every one of them partake, and so become this or that species', as Locke 9.10 described the notion. The idea in the present enquiry is not of any such `natural essences' apart from particulars, but of the (essential) natures of particulars. We want to describe the nature which includes what a particular thing is, the principle of any changes it may go through, and that by which it may be intelligible to us.       9.4.4 Elements We have above that the ultimate substances are really forms of potentiality, or `forms of propensity' to give a more commonly used description.   This is a extension of Aristotle's approach (described in section 3.3) if we take `propensity' to be his underlying matter. His general principle about elements is that they are the underlying matter in forms of combinations of prime qualities.   As in Wallace [1967], the elements are thus the underlying propensity in forms described by combinations of prime qualities, and these basic qualities could be electric charge, spin, `quark colour', etc.   The elements, therefore, could reasonably be the different kinds of electrons and quarks. Aristotle's natures and potentialities of the elements could be explained as the different operations of their particular forms of propensity.         9.4.5 On Time and Change To conclude this chapter, I should point out again a certain `unconventionality' about the logic of actualities and potentialities as it has developed. In classical physics, what are `actual' are the corpuscles themselves, but (for a variety of reasons) that view is no longer satisfactory. Now, the actualities produced after a change are not the new substances (for substances are forms of propensity), but are the `remains' of the previous propensities (the previously interacting substances) at previous places in space-time. That is, the actualities produced are always in the past region of space-time, compared to where there are propensities still operative. The effects of actualising, therefore, are not just in the past; it is just that the past is the only place where there can be pure actualities. The present places have a limited version of the previous propensities for events there, and so do not contain actualities (yet). This is perhaps unconventional, even odd to some extent, but in no other way, I argue, can changes and actualising be intelligibly comprehended.   This view of actualising also makes it advisable that there be some indeterminism (no matter how small), in order to distinguish actualities from potentialities. If there is some indeterminism, then actualities (as fully determinate particulars) can be distinguished from potentialities (as partially determinate particular fields). Determinism could perhaps be accommodated, by introducing some other distinction between actualities and potentialities, but that would be an unwelcome complication to the story.

    

Author: I.J. Thompson (except as stated)

Email: IJT@generativescience.org