Common philosophical discussions concerning the ethics of human interaction with the biosphere and universe have been significantly informed by certain presuppositions: nature is conquerable; human cultural and social progress is somewhat like a thing, beyond human control, and is inevitable and benevolent; and Homo sapiens is the superior life-form. Although arguments, such as whether humans should conquer nature, founded upon these presuppositions have sometimes been challenged, each of these three presuppositions wants direct analysis. The three have become so ingrained in (...) professional and everyday discourse that they have mythic proportions, as though beyond question. Because of the weightiness of the relevant philosophical issues, they merit overt analysis. Although they are independent and may be analyzed separately, this article treats them as whole, as they often work together in arguments. After finding substantial problems, the article suggests alternative ways of building sustainable presuppositions in similar territory. (shrink)