The paper investigates the epistemic conception of quantum states---the view that quantum states are not descriptions of quantum systems but rather reflect the assigning agents' epistemic relations to the systems. This idea, which can be found already in the works of Copenhagen adherents Heisenberg and Peierls, has received increasing attention in recent years because it promises an understanding of quantum theory in which neither the measurement problem nor a conflict between quantum non-locality and relativity theory arises. Here it is argued (...) that the main challenge for proponents of this idea is to make sense of the notion of a state assignment being performed correctly without thereby acknowledging the notion of a true state of a quantum system---a state it is in. An account based on the epistemic conception of states is proposed that fulfills this requirement by interpreting the rules governing state assignment as constitutive rules in the sense of John Searle. (shrink)

There is widespread belief in a tension between quantum theory and special relativity, motivated by the idea that quantum theory violates J. S. Bell’s criterion of local causality, which is meant to implement the causal structure of relativistic space-time. This paper argues that if one takes the essential intuitive idea behind local causality to be that probabilities in a locally causal theory depend only on what occurs in the backward light cone and if one regards objective probability as what imposes (...) constraints on rational credence along the lines of David Lewis’ Principal Principle, then one arrives at the view that whether or not Bell’s criterion holds is irrelevant for whether or not local causality holds. The assumptions on which this argument rests are highlighted, and those that may seem controversial are motivated. (shrink)

Einer weit verbreiteten Auffassung zufolge ist es eine zentrale Aufgabe der Philosophie der Mathematik, eine ontologische Grundlegung der Mathematik zu formulieren: eine philosophische Theorie darüber, ob mathematische Sätze wirklich wahr sind und ob mathematischen Gegenstände wirklich existieren. Der vorliegende Text entwickelt eine Sichtweise, der zufolge diese Auffassung auf einem Missverständnis beruht. Hierzu wird zunächst der Grundgedanke der Hilbert'schen axiomatischen Methode orgestellt, die Axiome als implizite Definitionen der in ihnen enthaltenen Begriffe zu behandeln. Anschließend wird in Anlehnung an einen Wittgenstein'schen Gedanken (...) zur normativen Rolle mathematischer Sprache argumentiert, dass im Kontext der Hilbert'schen Axiomatik mathematische Sätze als Standards für die Verwendung der in ihnen enthaltenen Begriffe dienen und dass dies die Idee einer ontologischen Grundlegung für die Mathematik untergräbt. (shrink)