In developing our understanding of function and functional entities, we have referred repeatedly to the "life requirements" of organisms. A simpler word for this essential concept is need. A need is a thing that is required to maintain or enhance the life of an organism. In this precise sense of the word, a need is something objectively necessary to the life, health, or well-being of the organism, to be distinguished carefully from a desire. Frequently, the things we desire are also things we need, but not every desire is truly a need. For example, a smoker may crave a cigarette. If he tells himself that he "needs" the cigarette, however, he is almost certainly deluding himself, since a considerable body of evidence indicates that this habit is potentially harmful to one's life and health, possibly lethal, and decidedly not beneficial. (In recognizing these harmful effects, it must be emphasized, we do not seek to limit the smoker's freedom of choice, which involves higher-level principles of broader significance, explored later in this course.)

This case provides an excellent illustration of the necessity of maintaining clear, valid concepts if we are to achieve a full, unobstructed awareness of reality. For the smoker, distinguishing clearly between need and desire may be an essential step toward overcoming a destructive habit.