Crusoe Analysis
We begin to develop basic praxeological concepts by examining the activities of Robinson Crusoe, alone on an island. As we have already seen (cf. pp. 2.4:3-14), human action in general arises from individual action; consequently, we must understand the latter before we can understand the former. Thus an analysis of actions of an isolated individual is our most logical beginning point. The most basic premise of praxeology is that every human acts to maximize his or her own purposes, within the context of his or her personal knowledge and understanding. This premise, of course, is consistent with an important principle developed in Section 2—namely, that human action arises from individual purposes. We do not assume that those personal purposes are always rational or consistent with an individual's objective values. Crusoe may not always pursue his self-interest, in the sense just discussed in our investigation into ethics. As we shall continue to emphasize, praxeological analysis applies equally well to the egoist, the altruist, the egotist, and the hedonist. It applies to Crusoe in isolation, but also to multiple individuals acting cooperatively to achieve a common goal.

Praxeology develops from the above premise, together with certain corollaries deriving from our "common-sense" understanding of the concepts of purpose, maximize, and knowledge.