[jmherbener]

In both the case of human action and the case of complex physical phenomenon, there is the problem that the “facts” available to empirically test hypotheses are themselves complex, i.e., generated by the complex set of causal factors, and not simple facts, i.e., generated by a controlled experiment in which only one causal factor is permitted to change.

The additional problem in the case of human action is that it may not be possible to give an entirely material explanation of human valuing and choosing, whereas it is possible, at least in theory, to give an entirely material explanation of physical phenomenon.

Take a look at Ludwig von Mises’s book Human Action, pp. 30-32 and 17-18.

http://mises.org/books/humanactionscholars.pdf