For instance, a human being has a very urgent need for oxygen. Since oxygen is readily available in the atmosphere, however, humans need not normally take special action to procure it (although they must process it through respiration). In most situations, therefore, oxygen is not a goal of action and hence does not have "value" (in either sense of the word). Of course, oxygen may acquire value in habitats removed from the earth's atmosphere, such as undersea or space colonies. Moreover, pure oxygen may be valuable in scientific settings.

The inverse relationship between value and availability will become important in Section 4, where we shall see how "value" as a goal of human action gives rise to market value. While we do not encounter oxygen vendors on every terrestrial street corner, this vital gas might well command a high market value in an artificial environment.