Abstract: What is our conception of the temporal priority of cause over effect? It is that a causal chain runs always in the earlier-to-later direction. Each link in the chain is a process, whose initiation is the immediate, and thus simultaneous, effect of the arrival at a particular stage of the process that constitutes the preceding link. It is the fact that it is the subsequent continuation of the process, once initiated, that calls for no explanation, which gives a temporal direction to the causal chain. If there are causal chains running in the reverse as well as in the usual direction, there is a possibility of causal loops.

Keywords: Aquinas backward causation, causal explanation, causation, fatalism, time,