Scriven and MacKay on Unpredictability and Free Choice

Abstract

Consider the questions of how much freedom or how much unpredictability would be in human behaviour on the hypothesis that determinism is true. These seem to be conceptual questions, as opposed to empirical ones, since the issue is not whether determinism actually applies to human beings, but rather whether determinism is logically compatible with unpredictability and freedom. I propose to argue, however, that the discussions of these issues by Michael Scriven and D. M. MacKay are not based solely on conceptual premises, but rather presuppose an empirical premise. I will argue further that the only available way of supporting this premise makes the doctrine of unpredictability relatively uninteresting, and leads to an untenable view of free choice because the agent cannot control which particular choice results. I will begin with Michael Scriven's doctrine that because of contrapredictive motivation, there is an essential unpredictability in human behaviour.' The situation which Scriven discusses is the following. A predictor makes a prediction about an agent on the basis of his knowledge of the relevant initial conditions and laws. The agent, however, is motivated to falsify the prediction, and acts so that the prediction fails. The agent may do this whether or not the predictor tells him the prediction, since he can replicate the prediction: for there is no reason to suppose that the predictor has greater ability in obtaining knowledge of the initial conditions and in using the relevant laws to obtain the prediction. In order to sort out the issues involved in regard to contrapredictivity, I will distinguish one rather complex conceptual issue and three empirical issues: