István Aranyosi

Leibniz notoriously insisted that no two individuals differ solo numero, that is, by being primitively distinct, without differing in some property. The details of Leibniz’s own way of understanding and defending the principle –known as the principle of identity of indiscernibles (henceforth ‘the Principle’)—is a matter of much debate. However, in contemporary metaphysics an equally notorious and discussed issue relates to a case put forward by Max Black (1952) as a counter-example to any necessary and non-trivial version of the principle. Black asks us to imagine, via one of the fictional characters of his dialogue, a world consisting solely of two completely resembling spheres, in a relational space. The supporter of the principle is then forced to admit that although there are ex hypothesi two objects in that universe, there is no property (except trivial ones), not even relational ones, to distinguish them, and hence the necessary version of the principle is falsified. In this essay I will argue that Black’s possible world, together with the dialectic between the potential friends and foes of the Principle as expounded by Black himself..

Ordinary people tend to be realists regarding perceptual experience, that is, they take perceiving the environment as a direct, unmediated, straightforward access to a mindindependent reality. Not so for (ordinary) philosophers. The empiricist influence on the philosophy of perception, in analytic philosophy at least, made the problem of perception synonymous with the view that realism is untenable. Admitting the problem (and trying to offer a view on it) is tantamount to rejecting ordinary people’s implicit realist assumptions as naive. So what exactly is the problem? We can approach it via one of the central arguments against realism – the argument from hallucination. The argument is intended as a proof that in ordinary, veridical cases of perception, perceivers do not have an unmediated perceptual access to the world. There are many versions of it; I propose the following1: 1. Hallucinations that are subjectively indistinguishable from veridical perceptions are possible. 2. If two subjective states are indistinguishable, then they have a common nature. 3. The contents of hallucinations are mental images, not concrete external objects. 4. Therefore, the contents of veridical perceptions are mental images rather than concrete external objects. The key move is, I believe, from the fact that hallucinations that are subjectively indistinguishable from cases of veridical perception are possible to an alleged common element, factor, or nature, in the form of a mental state, in the two cases – that is, premise 2. Disjunctivism, at its core, can be taken as simply denying this move, and arguing that all that follows from the premise stating the possibility of hallucinations that are subjectively indistinguishable from cases veridical perception is that there is a broader category, that of “experience as of...”, which encompasses both cases..

Tobias Hansson Wahlberg argues in a recent article (2009) that the truth of “Hesperus is Phosphorus” depends on the assumption that the endurance theory of persistence is true. The statement is not true (or at least can reasonably be doubted), he argues, if one assumes (a) the theory of persistence according to which objects are four-dimensional entities, persisting through perdurance, i.e. by having temporal parts that are numerically distinct, and (b) the thesis of unrestricted mereological composition (UMC), that is, that any two things, however scattered in space or time, compose a sum.

In this article, I undertake the tasks: (i) of reconsidering Feigl’s notion of a ‘nomological dangler’ in light of recent discussion about the viability of accommodating phenomenal properties, or qualia, within a physicalist picture of reality; and (ii) of constructing an argument to the effect that nomological danglers, including the way qualia are understood to be related to brain states by contemporary dualists, are extremely unlikely. I offer a probabilistic argument to the effect that merely nomological danglers are extremely unlikely, the only probabilistically coherent candidates being ‘anomic danglers’ (not even nomically correlated) and ‘necessary danglers’ (more than merely nomically correlated). After I show, based on similar probabilistic reasoning, that the first disjunct (anomic danglers) is very unlikely, I conclude that the identity thesis is the only remaining candidate for the mental–physical connection. The novelty of the argument is that it brings probabilistic considerations in favor of physicalism, a move that has been neglected in the recent burgeoning literature on the subject.