According to Jerry Fodor, “[h]uffing and puffing and piling on the teleology just doesn’t help with the disjunction problem; it doesn’t lead to univocal assignments of intentional content” (1990, p. 72). That Fodor separates these two claims with only a semicolon is unfortunate, for each merits individual scrutiny. First, there is the claim that appeals to the theory of evolution by natural selection will not help with the disjunction problem. I will argue that the truth of this claim depends upon how we characterize the relation between a representational state and that which it is about Fodor assumes this relation must be a causal one, and this assumption leads inevitably to the disjunction problem.

Psychological Externalism (PE) is the view that the contents of intentional psychological states are determined by factors external to the subject of those states. For example, PE holds that the content of a belief will be established at least in part by features of the environment, broadly construed, around and more or less detached from the believer. The range of such external factors is quite large, and various forms of PE emerge depending on which sorts of factors are endorsed. Generally speaking, these factors are those that establish the reference of the terms used to specify the contents of psychological states. To convey the flavour of this doctrine, let me briefly review some of the candidate external factors.

It seems intuitively obvious that metameric matching of color samples entails a loss of information. Metamers are distributions of wavelength and intensity (or “spectral energy distributions“) that perceivers cannot discriminate. Consider two color samples that are presented under ordinary white light and that appear to normal observers to be of the same color. It is well-established that such color samples can have quite different surface-reflective properties; e.g., two samples that appear to be the same shade of green may in fact reflect strikingly different patterns of wavelengths within the visible spectrum (see Figure 1). In this case, sameness of appearance under similar conditions of illumination does not entail sameness of surface reflectance. Spectrophotometrically diverse materials appear the same. It would seem then that information has been lost, that the visual system has failed in its task of chromatic discrimination.

It may be thought that the question ‘when is a physical theory relativistic?’ has a fairly straightforward answer, namely: ‘when it is Galilean invariant’ (for classical mechanics) or ‘Lorentz invariant’ (for special relativity). In the context of the modern ‘spacetime theory’ approach to relativity physics, the answer is more elaborate, in the interests of greater precision. In this paper, we examine two recent discussions of the issue, or aspects of it, found in a 1990 paper of Arntzenius and the well-known 1983 study of Friedman.

Arntzenius constructs a ‘sure-fire method’ of constructing a Lorentz invariant spacetime theory from a non Lorentz invariant one. We argue that if the original theory is anything like a typical dynamical theory in physics, its ‘completeness’—in a sense to be defined—will render the new theory underdetermined.

Leibniz indiscernibility argument: If the points of space or space-time are real, then shifting everything by a geometric symmetry transformation f (e.g., translation or rotation) produces a physically different situation, since the same bodies or events now occupy different points: whatever occupied point p now occupies the distinct point fp. This may violate identity of indiscernibles, or other principles of verifiability or theoretical parsimony.

Leibniz’s f was a symmetry of Euclidean space E, so the argument seems inapplicable to the inhomogeneous space-times of GTR. However, the underlying manifold M always possesses symmetries f, so one may take f also to move the geometric structure across M, along with the physical objects and events. The resulting variant models still represent physically distinct worlds, since the objects and geometric structure formerly at p are now at fp. Indeed there is more variability, since M has far more symmetries than E.

In 1905 Einstein derived the Lorentz transformations linking inertial coordinate systems. He took as his central principles the relativity principle (RP) and the light postulate (LP), and assumed along the way a symmetry that has become known as ‘spatial isotropy’ (Berzi and Gorini 1969). This symmetry will be defined below but it basically requires that boosting has the same effect whether to the right or left or to the north or south etc. Since it really is a symmetry about boosts I shall call it ‘boost isotropy'.

The purpose of this paper is to explore the relativistic kinematics (both Einsteinian and Galilean) resulting from implementing RP but breaking with the venerable tradition of implementing ‘boost isotropy’.

In recent years there has been renewed discussion of the problem of temporal becoming (Maxwell 1985,1988; Dieks 1988; Stein 1991). The theme of this paper is that these discussions, timely and interesting as they are, do not go deeply enough into the question. I would like to suggest that a certain way of thinking about simultaneity, which as far as I know was first sketched in a science fiction novel by Robert A. Heinlein (1956), opens up a set of possibilities that deserve serious consideration.

More precisely, I will address the following question: is there anything in the formal structure of Minkowski spacetime which corresponds to our intuitive albeit imprecise notion of a global “present”? It is generally assumed that because of the relativity of optical simultaneity the answer to this question is, resoundingly, no.