Auguste Comte's doctrine of the three phases through which sciences pass (the theological, the metaphysical, and the positive) allows us to explain what John Stuart Mill was attempting in his magnum opus, the System of Logic: namely, to move the science of logic to its terminal and 'positive' stage. Both Mill's startling account of deduction and his unremarked solution to the Humean problem of induction eliminate the notions of necessity or force—in this case, the 'logical must'—characteristic of a science's metaphysical (...) stage. Mill's treatment had a further surprising payoff: his solution to the Problem of Necessity (what today we call the problem of determinism and freedom of the will). (shrink)