Determinism presents us with a sceptical problem by casting doubt upon the basic common sense conviction that we are free agents who are, on occasion, confronted with genuine alternatives. A genuine alternative is present in a situation in which an agent must choose between two actions, each of which he can both select and perform. Which of the actions he chooses and does is determined at the moment of his decision, but not prior to it. The non-determinist hangs steadfastly onto this conviction and seeks to bolster it by common sense arguments; yet the arguments of the determinist are so clear, simple and “scientific” that the would-be libertarian often finds himself at a loss. In this paper I shall argue that the seemingly irrefutable arguments of the determinist rest upon an implicit assumption which is inconsistent with determinism. This assumption is a quasi-Kantian one: that a human being is a rational agent who, on occasion, acts on the basis of reasons which justify but do not causally explain his action. The relation between the reason and the action which it justifies is logical rather than causal. Although the determinist explicitly rejects this assumption, he also holds determinism to be objectively true and supports his claim by appealing to justifying reasons. I shall argue that it is a logical consequence of determinism that appeals to justifying reasons and also the very concept of objective truth must be abandoned.