The concept of life, which gives rise to the concept of need, refers not just to a minimal "survival" level of existence, but to the totality of an organism's "self-sustaining and self-generated action." Higher organisms are organized in elaborate hierarchies: organelles within cells within tissues within organs within complex systems. Although impaired function in any of the subordinate parts may not cause instant death for the organism, it tends to weaken it, increasing the potential for premature death. Proper function and integration of all the parts is therefore vital to the life of the organism. Insofar as all of its parts function properly and in harmony, an organism is said to be healthy. Thus a living entity is not only "alive" or "dead," but may also be living on a higher or lower level. A healthy plant, for instance, does not merely survive, but thrives, shooting out new branches, leaves, and tendrils. Several recent philosophers have used the term "flourishing" to describe a comparable high-level state of existence in humans.

Hence the requirements of health, including the optimal functioning of each of an organism's component systems, must be included among its needs. Needs, like life itself, involve more than "bare necessity": they involve living on the highest, healthiest, and most fully integrated level possible.