At its best, the quest for sustainable use of the planet aspires to a harmonious relationship between human society and natural systems. At its worst, sustainable use is an assertion that human ingenuity and technology can free humankind from biophysical constraints and its dependence upon ecological life support systems. Although science guided by reason is essential to reaching informed decisions on sustainability, it must be accompanied by a new ethos, or set of guiding beliefs. Science can never reduce uncertainty on the complex multivariate systems called ecosystems to the degree that explicit legislation would be possible to protect the components on a species by species, habitat by habitat, ecosystem by ecosystem, and landscape by landscape basis without going to ridiculous extremes. This circumstance does not, however, invalidate attempting to define conditions appropriate to achieving sustainability. Some consensus must be reached on the broad, general conditions governing human society's relationship to the environment. A shared ethos would promote sustainable use and reduce the possibility of harsh penalties exacted upon species that do not respond adequately to alteration in their environment.