David Hume (1711–76) described the question of liberty and necessity as "the most contentious question of metaphysics, the most contentious science".¹ He was right about it being contentious. Whether it is metaphysical is another matter. I think that what is genuinely metaphysical is an assumption that Hume, and a good many other philosophers, make in their treatment of the question. The assumption is about language and reality. I call it "the conformity assumption". But more about that shortly. Let us begin at the obvious beginning, by considering what the terms "liberty" and "necessity" mean in the expression "liberty and necessity".