There was a time when it seemed that we understood determinism. If a system of differential equations had a unique solution for a given set of boundary and initial conditions, then the entire future evolution of the system in question was thereby determined. In a deterministic world, predictability was guaranteed, at least in principle, despite the complexities and vagaries of large scale observation. Beneath these surface generalizations there was a world of order and clarity whose workings could be gleaned by controlled experiment and observation. In such a world, chance lay only on the surface of things, the result of ignored forces and imprecise reckonings.
Chaos theory has changed this picture considerably-some would say so drastically that determinism is no longer recognizable. Even within the rigid confines of the determinism, chance has been elevated from a by-product of human ignorance to a fundamental ontological feature of reality. In this essay, I shall examine some of the results in chaos theory that have led to this view, and critically examine the claim that chaos theory has not only legitimized chance ontologically, but has ended in making it indistinguishable form determinism itself.