Because human beings seek goods for their potential services to their various purposes, those purposes must guide us in distinguishing among goods and in determining the appropriate unit for each good in an analysis. In many cases the services that a good can provide may depend on the context. For instance, ice in the summertime may be able to fulfill services that ice in the winter could not fulfill; consequently, the two should be considered different goods in praxeological analysis.

A unit of a good is the smallest quantity of the good that satisfies all of the ends for which it is sought by the individuals in an analysis. Suppose that one of the purposes for which oxen are valued is pulling a plow, for example, and that a team of four oxen would be required for that objective. The appropriate unit for analysis is then not one ox, but four oxen—or possibly more, depending on other possible uses for the animals. Our definition of "unit" is consistent with the way appropriate units are determined in other fields. In chemistry, the basic unit of oxygen is the atom, which is the smallest quantity of the element that possesses oxygen's characteristic chemical properties. An oxygen molecule is too large to explain oxygen's behavior in chemical reactions, while a proton would be too small. Similarly, in praxeology the most basic property of a good is the services it provides to human actors. A quantity of the good insufficient to provide all of its desired services would not be an appropriate unit for analysis. The proper unit, of course, may vary according to context.