Hilary Putnam's work has been original, technically proficient, relevant to broad human concerns, widely influential — and subject to unexpected sharp turns. He invented the computational functionalist view of the mind, showed how to make it precise, related it to wider issues, saw it become the received view — and then turned against it, eloquently urging its rejection. He put forward a new conception of scientific realism, worked out technical details, suggested its wider significance, helped make it prominent in epistemology and philosophy of science — and then became its foremost critic. If Putnam's work did not have so many virtues, such sharp turns in his thought (of which these are only two examples) would suggest a philosopher unable to develop a stable view or unwilling to be serious. But the radical shifts in Putnam's thought are not signs of instability or frivolity, nor of carelessness or faddishness. They rather manifest a sensitivity to underlying shifts in the intellectual and philosophical climate of our time, rooted in an acute sense of when and how fashionable ways of thinking have gone wrong and are leading nowhere.