Causality is the basic idea that all events have causes. When every cause is determined completely by prior causes, it leads to the idea of determinism. A causal chain links all events to earlier events in a limitless sequence. Theologians inconsistently imagine the chain to break with an uncaused cause (causa sui) which they identify with God. Quantum indeterminacy produces uncaused causes. There is still a causal chain, but it does not permit complete predictability. Events are now merely probable, no longer certain, though the probability can be arbitrarily close to certainty. Most macroscopic events are, for practical purposes, as predictable as complete determinism would have allowed. For chaotic processes, this may quite unpredictable.