Hans Reichenbach's Philosophic Foundations of Quantum Mechanics (1944) has attracted the attention of philosophers because of its proposal for the interpretation of the theory in terms of a non-standard, threevalued logic.¹ Such an interpretation is, as Reichenbach calls it, a "restrictive" one; that is, it leaves certain propositions formulable in the language of the theory without standard truth conditions.² These propositions can be neither verified nor falsified, and the facts they express thus neither predicted nor explained by the theory. A typical such proposition assigns a determinate position and momentum to a particle at some instant. Clearly, embracing such an interpretation involves renouncing a spacetime description of the world, and is thus not to be entered into lightly.