Dummett and others have failed to show that an effect can precede its cause. Dummett claimed that ‘backwards causation’ is unproblematic in agentless worlds, and tried to show under what conditions it is rational to believe that even backwards agent-causation occurs. Relying on considerations originating in discussions of special relativity, I show that the latter conditions actually support the view that backwards agent-causation is impossible. I next show that in Dummett’s agentless worlds explanation does not necessitate backwards causation. I then show why even relative backwards causation is impossible in his and Tooley’s scenarios of parallel processes in which causes apparently act in opposite temporal directions. We thus have good reasons for thinking that backwards causation is impossible.