Critics of planned economies argue that planners cannot detect consumer preferences, shortages and surpluses with sufficient accuracy and therefore cannot efficiently co-ordinate production (in a market economy, a free price system is intended to serve this purpose). This difficulty was notably written about by economists Ludwig von Mises and Friedrich Hayek, who referred to subtly distinct aspects of the problem as the economic calculation problem and local knowledge problem, respectively. Whereas the former stressed the theoretical underpinnings of a market economy to subjective value theory while attacking the labor theory of value, the latter argued that the only way to satisfy individuals who have a constantly changing hierarchy of needs and are the only ones to possess their particular individual's circumstances is by allowing those with the most knowledge of their needs to have it in their power to use their resources in a competing marketplace to meet the needs of the most consumers most efficiently. This phenomenon is recognized as spontaneous order. Additionally, misallocation of resources would naturally ensue by redirecting capital away from individuals with direct knowledge and circumventing it into markets where a coercive monopoly influences behavior, ignoring market signals. According to Tibor R. Machan: "Without a market in which allocations can be made in obedience to the law of supply and demand, it is difficult or impossible to funnel resources with respect to actual human preferences and goals".