Relativity and the order of cause and effect in time

Signal velocities greater than that of light are well known to be ruled out by a combination of the theory of relativity and causality, because their existence would lead to the possibility of causal cycles. We exhibit the reason for this prohibition and analyze the relevant aspects of the notion of causality. We argue that the logical basis of the distinction between cause and effect is not their temporal order, but that it rests on the issue of control. We then examine the notion of control in this context.