Condorcet wrote in 1794, 'The sole foundation for belief in the natural sciences is this idea, that the general laws dictating the phenomena of the universe are necessary and constant. Why should this principle be any less true for the development of the intellectual and moral faculties of man than for the other operations of nature?' In similar vein, Buckle speaks of the ‘undeviating regularity of the moral world’, which is part of ‘one vast scheme of universal order’. These sentiments catch what I take to be central to passive conceptions, the idea that human action is a natural and determined phenomenon. Our next task is to find the best account we can of causal explanation. Naturalism is the thesis that there is only one mode of explanation, and determinism the thesis that any fact which has an explanation is, together with some other fact, an instance of a natural law. It is therefore vital to understand the notion of a law. I shall present the task as one in epistemology. What is a natural law and how do we know when we have found one?

I grasp these nettles in hope, since I do not at all deny that the moral world has its regularities. Action has antecedents which sometimes wholly and always partly determine it in accordance with natural laws.