In Parts of Classes [Lewis 1991] David Lewis attempts to draw a sharp contrast between mereology and set theory and to assimilate mereology to logic. He argues that, like logic but unlike set theory, mereology is “ontologically innocent”. In mereology, given certain objects, no further ontological commitment is required for the existence of their sum. On the contrary, by accepting set theory, given certain objects, a further commitment is required for the existence of the set of them. The latter – (...) unlike the sum of the given objects – seems to be an abstract entity whose existence is not directly entailed by the existence of the objects themselves. The argument for the innocence of mereology is grounded on the thesis of “Composition as identity”. Lewis analyses two different versions of the thesis: the first is the Strong composition thesis, according to which certain objects are their sum, where the use of “are” would mean that composition is literally identity. The second version is the Weak composition thesis, according to which composition is analogous, under some aspects, to identity. He criticises the first version of the thesis and argues for the second one. In the paper we argue that (T1) arguments for the ontological innocence of mereology are not conclusive. An obvious objection to the Strong composition thesis is that – given certain objects Xs – they cannot be their sum because none of them is the sum. One could reply to this objection by observing that the “are” in the sentence “The Xs are their sum” is to be understood collectively and not distributively. But the crux is that the collective reading fails to generate a new entity, whereas mereology, in particular in Lewis’ use for the reconstruction of set theory as “megethology”, needs to consider sums as real objects. Besides, we contend that Lewis’ argument for the innocence of mereology based on the Weak composition thesis is a petitio principii. The reason is that the aspects of the analogy between composition and identity, which Lewis emphasises, obtain under the presupposition of the existence of sums. But this is just what a denier of innocence would refuse. (T2) Some arguments against the ontological innocence of mereology show a certain ambiguity in the innocence thesis itself. Some defences of the innocence seem to implicitly presuppose that the sum of certain objects Xs is not a genuine entity. Speaking of the sum of the Xs would be just another way of speaking plurally of the Xs. However, the relevant use of sums in mereology treats them as well determined objects. The relevant innocence thesis takes for granted that, though sums are genuine objects, nevertheless their existence does not require any further commitment. (T3) The innocence thesis, apart from Lewis’ defence, seems to depend on a general conception of the nature of objects and on how the notion of ontological commitment is understood. We think that the thesis is the manifesto of a realistic conception of parts and sums. This conception consists of the following clauses: (i) given any object x, it is well determined which parts it possesses; these are in turn objects whose existence is a necessary consequence of the existence of x. (ii) However any objects Xs are given, they automatically constitute a well determined object x which is their sum; (iii) We can refer singularly and plurally to parts and sums of given objects. Obviously, one might wonder if such a conception is really ontologically innocent. One could object that it is not innocent because clauses (i) – (iii) are not. For example, clause (i) could be considered as an ontological commitment to the existence of sums. But the innocence at issue does not concern the above-sketched conception. The innocence is embedded in the conception itself. In other words, someone who argues for clauses (i) – (iii) takes a point of view from which mereology appears to be innocent. For, such a point of view forces us to consider as well determined the parts of any object and does not allow us to separate the existence of certain objects form the existence of their sum. (T4) is the claim that the alleged innocence of mereology is subject to Quine’s notorious criticisms of the set-theoretical interpretation of second order logic. To the purpose, we construct a mereological model of a substantive fragment of set theory, i.e. the one that grounds the principal model semantics of second order logic. First, we construct a mereological model under the assumption of the existence of infinitely many atoms. Then, we replace this assumption with that of the existence of any infinite object (with or without atoms). Finally, let us make a general point about the innocence thesis of mereology. A conclusive argument for that would be a refutation of the thesis that there are only denumerably many entities. For, since the parts of an infinite object constitute a non-denumerable infinity, such an argument would entail that there could be no infinite without a non-denumerable infinity. However, the thesis that any genuine infinity is a denumerable one has had some important advocates. So, a conclusive argument for the innocence of mereology seems to be highly implausible. (shrink)

In Parts of Classes David Lewis attempts to draw a sharp contrast between mereology and set theory and he tries to assimilate mereology to logic. For him, like logic but unlike set theory, mereology is “ontologically innocent”. In mereology, given certain objects, no further ontological commitment is required for the existence of their sum. On the contrary, by accepting set theory, given certain objects, a further commitment is required for the existence of the set of them. The latter – unlike (...) the sum of the given objects – seems to be an abstract entity whose existence is not directly entailed by the existence of the objects themselves. The argument for the innocence of mereology is grounded on the thesis of composition as identity. In our paper we argue that: arguments for the ontological innocence of mereology are not conclusive. Some arguments against the ontological innocence of mereology show a certain ambiguity in the innocence thesis itself. The innocence thesis seems to depend on a general conception of the nature of objects and on how the notion of ontological commitment is understood. Specifically, we think that the thesis is the manifesto of a realistic conception of parts and sums. Quine‟s notorious criticism of the set-theoretical interpretation of second order logic seems to be reproducible against Lewis‟defence of mereology. To the purpose we construct a mereological model of a substantive fragment of set theory, adequate to ground the set-theoretical semantics of second order logic. (shrink)

Trinitarians claim there are three Divine persons each of which is God, and yet there is only one God. It seems they want three to equal one. It just so happens, some metaphysicians claim exactly that. They accept Composition as Identity: each fusion is identical to the plurality of its parts. I evaluate Composition as Identity's application to the doctrine of the Trinity, and argue that it fails to give the Trinitairan any options he or she didn't already have. Further, (...) while Composition as Identity does give us a new way to assert polytheism, its help requires us to endorse a claim that undercuts any Trinitarian motivation for the view. (shrink)

In , Peter van Inwagen asked a good question. (Asking the right question is often the hardest part.) He asked: what do you have to do to some objects to get them to compose something---to bring into existence some further thing made up of those objects? Glue them together or what?1 Some said that you don’t have to do anything.2 No matter what you do to the objects, they’ll always compose something further, no matter how they are arranged. Thus we (...) learned of the fusion of the coins in our pockets and the Eiffel tower. (shrink)

I endorse Composition as Identity, broadly and loosely understood as the thesis that a composite whole is nothing over and above its parts, and the parts nothing over and above the whole. Thus, given an object, x, composed of n proper parts, y1, ..., yn, I feel the tension between my Quinean heart and its Lewisian counterpart. I feel the tension between my obligation to countenance n+1 things, x and the y’s, each of which is a distinct portion of reality, (...) and my inclination to count just 1 thing, x, or just n things, the y’s, the former encompassing the same amount of reality as the latter. This paper is an attempt to reconstruct this tension and to explain it away without forgoing the intimate link between counting and countenancing. (shrink)

A plurality or plural object is a single object that is also many, and pluralitism is the thesis that there is such an object. This paper argues that pluralitism and closely related theses (e.g., the many-one identity thesis and the composition as identity thesis) violate logic. To do so, it formulates an approach to the logic and semantics of plural constructions that results in plural logic and relates treatments of plural constructions to accounts of natural number. And it gives a (...) critical examination of Frege’s views of numbers and plural constructions, and sketches the view of plural constructions as devices for talking about the many (as such), and an account of natural numbers as properties of a special kind, plural properties. (shrink)

In the thesis I offer an analysis of the metaphysical underpinnings of the extended cognition thesis via an examination of standard views of metaphysical building (or, dependence) relations. -/- In summary form, the extended cognition thesis is a view put forth in naturalistic philosophy of mind stating that the physical basis of cognitive processes and cognitive processing may, in the right circumstances, be distributed across neural, bodily, and environmental vehicles. As such, the extended cognition thesis breaks substantially with the still (...) widely held view in cognitive science and philosophy of mind, namely that cognitive processes and cognitive processing take place within the skin-and-skull of individual organisms. The standard view of metaphysical building relations can be expressed as the conjunction of two theses. First, that a metaphysical building relation – such as composition, constitution, realization, supervenience or emergence – is a relation of ontological dependence, because if a metaphysical building relation holds between X (or the Xs) and Y, then it is in virtue of X (or the Xs) that Y exists. Second, metaphysical building relations are synchronic (durationless) relations of ontological dependence. In the thesis, I propose an alternative diachronic framework by which to extend the standard synchronic accounts of metaphysical dependence relations, and by which to reformulate the metaphysical foundation of the extended cognition thesis. The project fills an important gap between analytical metaphysics (in particular, the metaphysics of dependence relations) and naturalistic philosophy of mind (especially the extended cognition thesis). To my knowledge there has been no attempt to establish a robust diachronic account of metaphysical building (or, dependence) relations such as, e.g., composition and constitution. However, this is precisely what I argue is required to properly advance and ground the metaphysics of extended cognition. Ultimately, my aim of reformulating the metaphysics of extended cognition consists in taking several steps toward a third-wave of extended cognition. (shrink)

This work presents and discusses the conception of instantiation as ‘partial identity’. The theory has been previously proposed in two different guises by Baxter and Armstrong . Attention will be paid mostly to Baxter’s presentation, which seems the best de veloped, and where instantiation is understood as identity of ‘aspects’ of a universal and a particular. The theory seems to offer a solution to the vexed question of Bradley’s Regress, because instantiation is no longer conceived as a relation between numerically (...) different entities. The proposed solution requires an ontology of ‘aspects’ in order to work. Aspects are presented in the form [ x insofar as j] where x is filled by the entity to which the aspect pertains and j is filled by the respect in which the entity in question is considered. Aspects are numerically identical with the entity to which they pertain and with the other aspects of the same entity. Aspects, nonetheless, are not mere ways in which one can conceive an entity. Aspects are objective. Rejection of the principle of indiscernibility of identicals is crucial to this theory. The attributions of one aspect are not also attributions to the other aspects of the same entity. Hence, aspects offer ways to deal with seemingly incoherent attributions to the same entity. Baxter uses them to solve the problem of the multi-location of universals, temporary intrinsics and trans-world identity, besides the nature of instantiation. Several difficulties are presented, both to the general metaphysics of aspects, and to the conception of instantiation as identity of aspects. In general: it is not clear how to distinguish objective aspects from the mere forms in which we conceive an entity; it is not clear what are the conditions of identity of an aspect; and although the necessity of identity is rejected in general, it reappears as necessity of ‘aspectual’ identity. The necessity of aspectual identity raises concerns about the stability of the view. In respect to the specific conception of instantiation as identity of aspects, it will be pointed out that the theory implies the complete identity of universals and particulars that instantiate them and, further, that it implies the identity of everything with everything. (shrink)

A critical survey of the fundamental philosophical issues in the logic and formal ontology of space, with special emphasis on the interplay between mereology (the theory of parthood relations), topology (broadly understood as a theory of qualitative spatial relations such as continuity and contiguity), and the theory of spatial location proper.