Jensen is primarily an advocate for wild nature and an opponent of civilization, rejecting the notion that it can ever be ethical or sustainable. He describes the linguistically and historically defensible definition of "civilization" as "a culture—that is, a complex of stories, institutions, and artifacts—that both leads to and emerges from the growth of cities ("civilization", see "civil": from "civis", meaning "citizen", from Latin "civitas", meaning "state" or "city")," and the definition of "city" as a group of "people living more or less permanently in one place in densities high enough to require the routine importation of food and other necessities of life." He explains that, by such definitions, civilizations and cities are both unsustainable: