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 reasonthose rules governing how we ought to believeare grounded in considerations of utility. I begin, in section 1, by offering an outline of Mill's account of '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. 2 All arts, Mill claims, are derived from the assumption that some object or state of affairs is valuable. "Every art has one first principle, or general major premise, not borrowed from science; that which enunciates the object aimed at, and affirms it to be a desirable object" (System, VIII: 949). "The art proposes to itself an end to be attained, defines the end, and hands it over to the science. The science receives it, considers it as a phenomenon or effect to be studied, and having investigated its causes and conditions, sends it back to art with a theorem of the combination of circumstances by which it could be produced" (System, VIII: 944). Each art is therefore formulated as an autonomous action-guiding body of rules, informed by a scientific understanding of the world, designed to bring about a specified end considered desirable: "[a]n art, or a body of art, consists of the rules, together with as much of the speculative propositions as comprises the justification of those rules" (System, VIII: 947). Mill offers the examples of "architecture" and the "medical arts". Architecture is the body of rules which aims at "beautiful or imposing" buildings; medicine is the body of rules which aims at the "preservation of health" (System, VIII: 949). We might term the ends of the individual arts proximate ends. Such ends, Mill notes, are not self-certifying, and can often come into conflict. The job of justifying and reconciling the ends set by the various arts-discerning their "place in the scale of desirable things", and determining what we should do, all things considered-is given to what he terms the "Art of Life" or "Practical Reason"