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The aim of this paper is to argue that there are categorical properties as well as causal powers, and that the world would not exist as we know it without them. For categorical properties are needed to define the powers—to locate them, and to specify their laws of action. These categorical properties, I shall argue, are not dispositional. For their identities do not depend on what they dispose their bearers to do. They are, as Alexander Bird would say, ’quiddities’. But there is nothing wrong with quiddities. And, in the second half of this paper, I shall defend the thesis that all categorical properties are quiddities.

This is a rewarding book. In terms of area, it has one foot firmly planted in metaphysics and the other just as firmly set in the philosophy of science. Nature's Metaphysics is distinctive for its thorough and detailed defense of fundamental, natural properties as essentially dispositional and for its description of how these dispositional properties are thus suited to sustain the laws of nature as (metaphysically) necessary truths.

Dispositional essentialists argue that physical properties have their causal roles essentially. This is typically taken to mean that physical properties are identical to dispositions. I argue that this is untenable, and that we must instead say that properties bestow dispositions. I explore what it is for a property to have such a role essentially. Dispositional essentialists argue for their view by citing certain epistemological and metaphysical implications, and I appeal to these implications to place desiderata on the concept of essence involved. I argue that the traditional modal theory of essence meets these desiderata, but that the resulting theory wrongly implies that certain dispositions essential to mass are essential to charge, thereby offering a new argument against modal theories of essence. I argue that dispositional essentialism requires a primitive notion of essence, and develop a primitivist theory based on Kit Fine's views. I show that the primitivist theory has all the virtues of the modal alternative, and none of the vices. I develop a novel way of thinking about the relationship between properties, laws and dispositions, and argue that it has distinct advantages over standard dispositional essentialist formulations.

Three basic positions regarding the nature of fundamental properties are: dispositional monism, categorical monism and the mixed view. Dispositional monism apparently involves a regress or circularity, while an unpalatable consequence of categorical monism and the mixed view is that they are committed to quidditism. I discuss Alexander Bird's defence of dispositional monism based on the structuralist approach to identity. I argue that his solution does not help standard dispositional essentialism, as it admits the possibility that two distinct dispositional properties can possess the same stimuli and manifestations. Moreover, Bird's argument can be used to support the mixed view by relieving it of its commitment to quidditism. I briefly analyse an alternative defence of dispositional essentialism based on Leon Horsten's approach to the problem of circularity and impredicativity. I conclude that the best option is to choose Bird's solution but amend the dispositional perspective on properties. According to my proposal, the essences of dispositions are determined not directly by their stimuli and manifestations but by the role each property plays in the structure formed by the stimulus/manifestation relations.

I will argue firstly that law-statements should be understood as attributing dispositional properties. Second, the dispositions I am talking about should not be conceived as causes of their manifestations but rather as contributors to the behavior of compound systems. And finally I will defend the claim that dispositional properties cannot be reduced in any straightforward sense to non-dispositional (categorical) properties and that they need no categorical bases in the first place.

This book advocates dispositional essentialism, the view that natural properties have dispositional essences.1 So, for example, the essence of the property of being negatively charged is to be disposed to attract positively charged objects. From this fact it follows that it is a law that all negatively charged objects will attract positively 10 charged objects; and indeed that this law is metaphysically necessary. Since the identity of the property of being negatively charged is determined by its being related in a certain way to the property of being positively charged, in any world in which these properties exist they must be related so that all negatively charged objects attract positively charged objects. 15 Bird opposes his dispositional essentialism to the view that properties are categorical in nature, with their identities grounded in quiddities that are not exhausted by their relations to other properties. The main exponents of this view are D.M. Armstrong and David Lewis. They take the laws of nature to be contingent though they entertain very different views about their nature: Armstrong is a necessitarian 20 about laws, taking them to be relations of nomic necessitation between universals, while Lewis is a Humean about laws who takes them to be a special kind of regularity. The book is a sustained defence of the dispositional essentialist conception of properties and laws against the competing conceptions espoused by Armstrong and Lewis. One rough way to characterize the difference between these conceptions is to say that 25 the categoricalist sees properties as passive and inert with the laws of nature being fixed independently of the nature of properties whereas, in contrast, the dispositional essentialist sees properties as active potencies from which the laws of nature automatically spring. A slightly more tendentious way to express the difference is to say, as Bird does, that the categoricalist views embrace the Humean doctrine that there are no 30 necessary connexions in nature, while the dispositional essentialist view, on the other hand, repudiates this doctrine..

A dispositional property is a tendency, or potency, to manifest some characteristic behaviour in some appropriate context. The mainstream view in the twentieth century was that such properties are to be explained in terms of more fundamental non-dispositional properties, together with the laws of nature. In the last few decades, however, a rival view has become popular, according to which some properties are essentially dispositional in nature, and the laws of nature are to be explained in terms of these fundamental dispositions. The supposed ability of fundamental dispositions to ground natural laws is one of the most attractive features of the dispositional essentialist position. In this paper, however, I cast doubt on the ability of dispositional essences to ground the laws of nature. In particular I argue that the dispositional essentialist position is not able to coherently respond?sympathetically or otherwise?to Cartwright's challenge that there are no true general laws of nature.

Those who hold that all fundamental sparse properties have dispositional essences face a problem with structural (e.g. geometrical) properties. In this paper I consider a further route for the dispositional monist that is enabled by the requirement that physical theories should be background-free. If this requirement is respected then we can see how spatial displacement can be a causally active relation and hence may be understood dispositionally.

Those who favour an ontology based on dispositions are thereby able to provide a dispositional essentialist account of the laws of nature. In part 1 of this paper I sketch the dispositional essentialist conception of properties and the concomitant account of laws. In part 2, I characterise various claims about the modal character of properties that fall under the heading ‘quidditism’ and which are consequences of the categoricalist view of properties, which is the alternative to the dispositional essentialist view. I argue that quidditism should be rejected. In part 3, I address a criticism of a strong dispositional essentialist view, viz. that ‘structural’ (i.e. geometrical, numerical, spatial and temporal) properties must be regarded as categorical.

: It is widely thought that dispositional properties depend upon categorical properties; specifying the nature of this dependency, however, has proven a difficult task. The dependency of dispositional properties upon categorical properties also presents a challenge to the thesis of Physicalism: If the physical sciences only tell us about the dispositional properties of the objects they study and if dispositional properties depend upon categorical properties, then it appears that there will be kind of property—categorical properties—that will escape description by the physical sciences. This paper argues that a new theory of dispositional and categorical properties, a theory put forth by C.B. Martin and John Heil, solves both of these problems: It presents a way of understanding the sense in which dispositional properties depend upon categorical properties that has major advantages over more popular accounts of this dependency and it also provides a new and interesting Physicalist response to the challenge presented by categorical properties.