ABSTRACT
Time was reversible in Newtonian mechanics, partly because we wanted it so. But we could have it so only under certain conditions. Not only does Newtonian mechanics deal in only second-order differential equations, but it is a discrete and determinist system. The influence of the Newtonian substructure has been the greater in that probability has often been viewed as a property of classes or ensembles, and classes are, by Bertrand Russell's thesis of extensionality, equated with their members. The time-reversibility of classical physics was a special, not a typical, feature. It was due, at least in part, to the special role played by substances, things. Quantum mechanics has no comparable concept of substance; and therefore can be less resistant to the real nature of time. Probabilities should be regarded not as partial truths about lots of things, expressed compendiously though incompletely, but as natural generalizations of the concepts of truth and falsity.
