What Primitive Substances Are There?

We have done nothing so far to establish that there are any primitive substances, but it is strongly arguable that there must indeed be at least some. For in the absence of any primitive substances, it appears, no other concrete objects could exist at all, including even places and times. All concrete objects which are not primitive substances are either composite substances or else non-substances. But how could these be all the concrete objects that exist? First, it couldn't be the case that all existing concrete objects are non-substances, because these, by definition, are all identity-dependent upon other concrete objects and yet, on pain of an infinite regress of a sort that is ruled out by the well-foundedness assumption of section 2 above, if any concrete object is to exist at all, one must exist which is not identity-dependent upon any other: that is, some substance must exist. But, secondly, not all substances could be composite substances, it seems, because this too would require there to be infinite descending chains of objects standing in relations of existential dependency to one another (albeit dependency of the ‘generic’ variety rather than of the ‘strong’

variety). For every composite substance demands the existence of other concrete objects to serve as its component parts, and the asymmetry of part–whole relations implies that a composite object cannot itself be a part of one of its own components—so that the component parts of a composite substance, if they are composite substances themselves, demand the existence of yet other concrete objects to serve as their component parts.

How many primitive substances are there? The possibilities are exhausted by primitive monism and primitive pluralism, maintaining respectively that there is just one primitive substance and that there are many primitive substances. As to the nature of this substance or these substances, two further possibilities arise: the primitive substance or substances may be either physical or mental. Of course, if primitive monism is correct and there is just one primitive substance, then it must be either physical or mental; but if primitive pluralism is correct and there are many primitive substances, then either all of them could be physical, or all of them could be mental, or some could be physical and some mental.

A physical substance, as I understand this term here, is one which necessarily exists in both space and time. By contrast, I take a mental substance

to be one which only necessarily exists in time—so that if a mental substance exists in space at all, then it does so only contingently and derivatively, by virtue of some contingent relationship which it bears to physical objects of some kind, certain of whose spatial properties and relations it may be said to inherit through that relationship. Such a relationship may be termed ‘embodiment’.²⁰⁵

If the only primitive substances are mental substances, then it appears to follow that there are in fact no physical substances and that space is unreal. This is because in that case nothing will underivatively occupy space: primitive substances will not do so, because ex hypothesi they will all be mental and so exist in time alone, or if also in space then only contingently and derivatively, in virtue of being suitably related to other concrete objects which occupy space. But other concrete objects will only be able to occupy space in as much as the objects to which they owe their existence occupy space themselves: and in the case hypothesized this requirement cannot ultimately be satisfied, because no primitive substance will occupy space underivatively. So in that case nothing will occupy space, whence there will be no physical substances and indeed no space, because space itself owes its existence to the existence of concrete objects capable of occupying it.

If primitive physical substances do exist, then either there is just one of them or else there are many of them. The latter view may be called physical atomism and the former view physical holism. Modern physical science provides no basis for adjudicating satisfactorily between these two views, because it appears to favour both of them, despite their incompatibility. The root of this problem lies in the so-called ‘wave-particle duality’ at the heart of modern quantum physics, whereby basic physical phenomena can sometimes best be interpreted in line with ‘atomistic’ particle descriptions and sometimes best be interpreted in line with ‘holistic’ wave or field descriptions. According to the latter sort of account, it seems, the only primitive physical substance could be the entire physical universe as a whole, whereas according to the former sort of account individual fundamental particles would appear to qualify as primitive physical substances (though here we would do well to recall the findings of Chapter 3, which indicated that such particles can at best be regarded as what I there called ‘quasi-objects’). To the extent that the best-informed explanatory theories of modern physical science appear, inconsistently, to favour both atomism and holism, we may be inclined to doubt whether there are in reality any primitive physical substances—and consequently to doubt whether any physical substances at all really exist. We might be inclined to conclude

205 See further my Subjects of Experience, 37–8.

that matter and space are, at best, in Leibniz's phrase, phenomena bene fundata.

Are there any primitive mental substances—indeed, are there any mental substances at all? If primitive mental substances do exist, then again either there is just one of them or else there are many of them. The latter view may be called mental atomism and the former view mental holism (neither to be confused with similarly entitled doctrines concerning mental states and their contents). The most likely candidate for the status of a primitive mental substance is an individual self. That being so, mental holism would amount to a kind of solipsism and is to that extent a highly implausible doctrine. (Another kind of mental holism is the doctrine of the ‘world soul’, which is equally implausible.) And, indeed, there are plausible arguments to the effect that individual selves are primitive mental substances. That a self is a substance as defined earlier and moreover a non-composite substance whose identity over time is accordingly primitive or ungrounded, are all claims for which support can be mustered—as is the claim that selves necessarily exist in time but at most only contingently in space and are consequently mental substances. However, I shall not argue directly for these claims here.²⁰⁶

Although, as I have just said, we may seriously doubt the reality of physical substances and consequently the reality of space, we cannot likewise cogently doubt the reality of time (notwithstanding the spurious arguments of certain metaphysicians such as McTaggart, whose views I touched on in Chapter 4). For although the appearance of distance and so of space may conceivably be no more than an appearance (as Berkeley held), the appearance of change and so of time cannot be no more than an appearance—for even the appearance of change itself involves change, namely, change in the conscious experience of a subject or self.²⁰⁷ But if time is real, then at least some primitive substances existing in time must exist, for the reasons given earlier. And since we have reason to doubt whether these are physical substances, to that extent we have grounds for concluding that these primitive substances must be mental substances, with individual selves constituting the most plausible candidates.

206 But see further ibid. ch. 2.

207 Cf. P. T. Geach, Truth, Love and Immortality: An Introduction to McTaggart's Philosophy (London: Hutchinson, 1979), ch. 7.