According to Mises there are three general requisite conditions to human action:
First, in order for a human to begin to act, they must first feel some uneasiness; second, they must imagine a more satisfactory state than the present one; third, they must expect that their purposeful behavior can reduce their uneasiness.
On the other hand, when it comes to “all thinkable conditions,” Mises adds that because science aims at allowing us a grasp of reality, praxeology mainly examines the conditions that occur in reality. Even when Austrian economists conduct peculiar thought experiments, they always stress that the purpose is to isolate in their analysis a factor that is obscured in the real world by a multitude of other factors.
They add additional realistic empirical statements such as the fact that people differ from each other and are changeable in time, that they treat free time as a valuable good, and that every action is a process that takes place in time.
There are, however, two instances in which Mises allows for the use of praxeology while assuming conditions that do not exist and do not match present reality. The first instance is an analysis of conditions that may arise in the future. For example, praxeology may explain the operation of a completely unregulated, that is fully free, market. In the second instance Mises allows for the analysis of unreal conditions that could not ever exist in the future, provided that such an analysis can help understand reality. Suppose that we want to show the validity of the contention that goods are scarce. To do that, we can assume that this contention is false and confront the result with reality, delineating differences between these two worlds.
All in all, praxeology is an aprioristic science, not unlike mathematics and logic. At the same time, its contentions are empirical. In spite of claiming, in contrast with Rothbard, that the axiom of human action is a priori, Mises acknowledged that other assumptions of praxeology are empirical, and that they help to shape and define its proper subject of analysis. Experience thus helps economists to focus on the subject of their investigations, but does not define their mode of operation. And the mode of operation, the method of analysis, is a priori.
Rothbard explains the process of verbal deduction clearly: “Furthermore, since praxeology begins with a true axiom, A, all the propositions that can be deduced from this axiom must also be true. For if A implies B, and A is true, then B must also be true.” Then he provides examples of such deduction, well worth quoting here: