The principle of sujjicient reason asserts that anything that happens does so for a reason: no definite state of ajfairs can come into being unless there is a sujjicient reason why that particular thing should happen. This principle is usually attributed to Leibniz, although the jirst recorded Western philosopher to use it was Anaximander of Miletus. The demand that nature be rational, in the sense that it be compatible with the principle of sujjicient reason, conflicts with a basic feature of contemporary orthodox physical theory, namely the notion that nature ’s response to the probing action of an observer is determined by pure chance, and hence on the basis of absolutely no reason at all. This appeal to pure chance can be deemed to have no rational fundamental place in reason-based Western science. It is argued here, on the basis of other basic principles of quantum physics, that in a world that conforms to the principle of sujjicient reason, the usual quantum statistical rules will naturally emerge at the pragmatic level, in cases where the reason behind nature ’s choice of response is unknown, but that the usual statistics can become biased when the reason for the choice is empirically identwable. It is explained here that u" the statistical laws of quantum mechanics were to be biased in this way then the basically forward-in-time unfolding of empirical reality described by orthodox quantum mechanics would generate the appearances of backward-timeeffects ofthe kind that have been reported in the scientmc literature.