In the Ultimate Foundation of Economic Science, Mises wrote,
"Thymology is a branch of history or, as Collingwood formulated it, it belongs in 'the sphere of history.' It deals with the mental activities of men that determine their actions. It deals with the mental processes that result in a definite kind of behavior, with the reactions of the mind to the conditions of the individual's environment. It deals with something invisible and intangible that cannot be perceived by the methods of the natural sciences. But the natural sciences must admit that this factor must be considered as real also from their point of view, as it is a link in a chain of events that result in changes in the sphere the description of which they consider as the specific field of their studies."
- Economic forecasts no better than a random walk by Sue Lannin, February 2013