theory argue that it is impossible to make accurate long-term predictions for highly complex systems such as an economy. Pierre-Joseph Proudhon raises similar calculational issues in his General Idea of the Revolution in the 19th Century, but he also proposes certain voluntary arrangements which would also require economic calculation. Leon Trotsky, a fierce proponent of decentralized economic planning, argued that centralized economic planning would be "insoluble without the daily experience of millions, without their critical review of their own collective experience, without their expression of their needs and demands and could not be carried out within the confines of the official sanctums" and "[e]ven if the Politburo consisted of seven universal geniuses, of seven Marxes, or seven Lenins, it will still be unable, all on its own, with all its creative imagination, to assert command over the economy of 170 million people". In contrast to the lack of a marketplace, market socialism can be viewed as an alternative to the traditional socialist model. Theoretically, the fundamental difference between a traditional socialist economy and a market socialist economy is the existence of a market for the means of production and capital goods. Socialist market abolitionists reply that whilst advocates of capitalism and the Austrian School in particular recognize equilibrium prices do not exist, they nonetheless claim that these prices can be used as a rational basis when this is not the case, hence markets are not efficient. According to market abolitionists socialists, decentralized planning allows for a spontaneously self-regulating system of stock control (relying solely on calculation in kind) to come about and that in turn decisively overcomes the objections raised by the economic calculation argument that any large scale economy must necessarily resort to a system of market prices. Suppression of economic democracy and self-management Central planning is also criticized by elements of the radical left. Libertarian socialist economist Robin Hahnel notes that even if central planning overcame its inherent inhibitions of incentives and innovation, it would nevertheless be unable to maximize economic democracy and self-management, which he believes are concepts that are more intellectually coherent, consistent and just than mainstream notions of economic freedom. As Hahnel explains: "Combined with a more democratic political system, and redone to closer approximate a best case version, centrally planned economies no doubt would have performed better. But they could never have delivered economic self-management, they would always have been slow to innovate as