The paper takes off from the problem of finding a proper content for the relation of identity as it holds or fails to hold among ordinary things or substances. The necessary conditions of identity are familiar, the sufficient conditions less so. The search is for conditions at once better usable than the Leibnizian Identity of Indiscernibles (independently suspect) and strong enough to underwrite all the formal properties of the relation.It is contended that the key to this problem rests at the (...) level of metaphysics and epistemology alike with a sortalist position. Sortalism is the position which insists that, if the question is whether a and b are the same, it has to be asked what are they? Any sufficiently specific answer to that question will bring with it a principle of activity or functioning and a mode of behaviour characteristic of some particular kind of thing by reference to which questions of persistence or non-persistence through change can be adjudicated.These contentions are illustrated by reference to familiar examples such as the human zygote, the Ship of Theseus and Shoemaker's Brown-Brownson. The first example is hostage for a mass of unproblematical cases. The problems presented by the second and third sort of examples arise chiefly (it is claimed) from an incompleteness in our conceptions of the relevant sort—the what the thing in question is. That incompleteness need not prevent us from knowing perfectly well which thing we are referring to. In the concluding section, sortalism is defended against various accusations of anthropocentrism.The paper touches on the interpretation of Heraclitus, Leibniz's theory of clear indistinct ideas, the difficulties of David Lewis's ‘perdurantist’ or stroboscopic view of persistence, four-dimensionalism, and the relation of personal identity both to experiential memory and to the particular bodily physiognomy of a subject. At some points—as in connection with the so-called Only a and b rule—the paper corrects, supplements or extends certain theses or formulations proposed in the author's Sameness and Substance Renewed (2001). (shrink)

This paper attempts to explain the emergence of the logical empiricist philosophy of space and time as a collision of mathematical traditions. The historical development of the ``Riemannian'' and ``Helmholtzian'' traditions in 19th century mathematics is investigated. Whereas Helmholtz's insistence on rigid bodies in geometry was developed group theoretically by Lie and philosophically by Poincaré, Riemann's Habilitationsvotrag triggered Christoffel's and Lipschitz's work on quadratic differential forms, paving the way to Ricci's absolute differential calculus. The transition from special to general relativity (...) is briefly sketched as a process of escaping from the Helmholtzian tradition and entering the Riemannian one. Early logical empiricist conventionalism, it is argued, emerges as the failed attempt to interpret Einstein's reflections on rods and clocks in general relativity through the conceptual resources of the Helmholtzian tradition. Einstein's epistemology of geometry should, in spite of his rhetorical appeal to Helmholtz and Poincaré, be understood in the wake the Riemannian tradition and of its aftermath in the work of Levi-Civita, Weyl, Eddington, and others. (shrink)

The interpretation of quantum mechanics is an area of increasing interest to many working physicists. In particular, interest has come from those involved in quantum computing and information theory, as there has always been a strong foundational element in this field. This paper introduces one interpretation of quantum mechanics, a modern ‘many-worlds’ theory, from the perspective of quantum computation. Reasons for seeking to interpret quantum mechanics are discussed, then the specific ‘neo-Everettian’ theory is introduced and its claim as the best (...) available interpretation defended. The main objections to the interpretation, including the so-called “problem of probability” are shown to fail. The local nature of the interpretation is demonstrated, and the implications of this both for the interpretation and for quantum mechanics more generally are discussed. Finally, the consequences of the theory for quantum computation are investigated, and common objections to using many worlds to describe quantum computing are answered. We find that using this particular many-worlds theory as a physical foundation for quantum computation gives several distinct advantages over other interpretations, and over not interpreting quantum theory at all. (shrink)

By inserting the dialogue between Einstein, Schlick and Reichenbach into a wider network of debates about the epistemology of geometry, this paper shows that not only did Einstein and Logical Empiricists come to disagree about the role, principled or provisional, played by rods and clocks in General Relativity, but also that in their lifelong interchange, they never clearly identified the problem they were discussing. Einstein’s reflections on geometry can be understood only in the context of his ”measuring rod objection” against (...) Weyl. On the contrary, Logical Empiricists, though carefully analyzing the Einstein–Weyl debate, tried to interpret Einstein’s epistemology of geometry as a continuation of the Helmholtz–Poincaré debate by other means. The origin of the misunderstanding, it is argued, should be found in the failed appreciation of the difference between a “Helmholtzian” and a “Riemannian” tradition. The epistemological problems raised by General Relativity are extraneous to the first tradition and can only be understood in the context of the latter, the philosophical significance of which, however, still needs to be fully explored. (shrink)

Paragraph 6 of Newton's Scholium argues that the parts of space cannot move. A premise of the argument -- that parts have individuality only through an "order of position" -- has drawn distinguished modern support yet little agreement among interpretations of the paragraph. I argue that the paragraph offers an a priori, metaphysical argument for absolute motion, an argument which is invalid. That "order of position" is powerless to distinguish one part of Euclidean space from any other has gone virtually (...) unremarked. It remains uncertain what the import of the paragraph is but it is not close to apparently similar arguments of Leibniz. (shrink)

Ajdukiewicz’s account of mathematical theories is presented and analyzed. Theories consist of primary and secondary theorems. Theories go through three phases or stages: preaxiomatic and intuitive, axiomatic but intuitive, axiomatic and abstract, whereas the final stage takes two forms: definitional and formal. Each stage is analyzed. The role of the concepts of truth, evidence, consequence, and existence is examined. It is claimed that the second stage is apparent or transitory, whereas the initial and final stages are vital and constitute two (...) salient attitudes to mathematics, focused on truth or consequence respectively. It is also claimed they are attitudes rather than stages, and the crucial difference between them concerns effectiveness. The chief question of philosophy of mathematics turns out to be to determine whether mathematical theories are assertive or hypothetical. (shrink)

Philosophy of physics is a small but thriving research field situated at the intersection between the natural sciences and the humanities. However, what exactly distinguishes philosophy of physics from physics is rarely made explicit in much depth. We provide a detailed analysis in the form of eleven theses, delineating both the nature of the questions asked in philosophy of physics and the methodology with which they are addressed.

In their paper, ‘When are thought experiments poor ones?’ (Peijnenburg and David Atkinson, 2003, Journal of General Philosophy of Science 34, 305-322.), Jeanne Peijnenburg and David Atkinson argue that most, if not all, philosophical thought experiments are “poor” ones with “disastrous consequences” and that they share the property of being poor with some (but not all) scientific thought experiments. Noting that unlike philosophy, the sciences have the resources to avoid the disastrous consequences, Peijnenburg and Atkinson come to the conclusion that (...) the use of thought experiments in science is in general more successful than in philosophy and that instead of concocting more “recherché” thought experiments, philosophy should try to be more empirical. In this comment I will argue that Peijnenburg’s and Atkinson’s view on thought experiments is based on a misleading characterization of both, the dialectical situation in philosophy as well as the history of physics. By giving an adequate account of what the discussion in contemporary philosophy is about, we will arrive at a considerably different evaluation of philosophical thought experiments. For I am convinced that we now find ourselves at an altogether decisive turning point in philosophy, and that we are objectively justified in considering that an end has come to the fruitless conflict of systems. We are already at the present time, in my opinion, in possession of methods which make any such conflict in principle unnecessary. What is now required is their resolute application. (Schlick, ‘The Turning Point in Philosophy’, 1930/1959, p. 54). (shrink)