In this article, I wish to argue that J.S. Mill holds that theoretical reason is subordinate to practical reason. Ultimately, this amounts to the claim that the norms of theoretical reason – those rules governing how we ought to believe – are grounded in considerations of utility. I begin, in Section 1, by offering an outline of Mill’s account of the ‘Art of Life’ (the body of rules governing how we should act), before turning in Section 2, to Mill’s account of the ‘Art of Thinking’ (the body of rules governing how we should believe). In Section 3, I suggest that, for Mill, the Art of Thinking is subordinate to the Art of Life, and that in an important sense, therefore, theoretical reason is subordinate to practical reason.