 An additional difference between explanations in terms of reasons and explanations in terms of causes, which some economists have emphasized, is that the beliefs and preferences that explain actions may depend on mistakes and ignorance (Knight 1935). As a first approximation, economists can abstract from such difficulties caused by the  intentionality  of belief and desire. They thus often assume that people have perfect information about all the relevant facts. In that way theorists need not worry about what people’s beliefs are. (If people have perfect information, then they believe and expect whatever the facts are.) But once one goes beyond this first approximation, difficulties arise which have no parallel in the natural sciences. Choice depends on how things look “from the inside”, which may be very different from the actual state of affairs. Consider for example the stock market. The “true” value of a stock depends on the future profits of the company, which are of course uncertain. In 2006 house prices in the U.S. were extremely inflated. But whether they were “too high” depended at least in the short run, on what people believe. They were excellent investments if one could sell them to others who would be willing to pay even more for them. Economists disagree about how significant this subjectivity is. Members of the Austrian school argue that these differences are of great importance and sharply distinguish theorizing about economics from theorizing about any of the natural sciences (Buchanan and Vanberg 1989, von Mises 1981).