Tugan-Baranovsky's ideas on socialism are reconstructed with an emphasis on the relation between political economy and utopia. Utopia enters the stage after the critique of capitalism, in the definition of the realm of possibilities in the world of ideas. With the help of ethics, the notion of ideal socialism, unreachable by definition, is defined in the sphere of utopia. Thus, the task of political economy is first to show which of these possible worlds are reachable in the real world, and second to choose the one that conforms better to ideal socialism: this is socialism in practice through the economic plan. Thus, far from considering utopia and science as contradictory, Tugan-Baranovsky saw them as complementary, and his socialism is the result of the dialogue he instituted between them.