Conducted 4 studies to show that the basic level differs qualitatively from other levels in taxonomies of objects and of living things. The 4 studies show that (1) parts prevail at the basic level, (2) basic level categories differ by parts, (3) subordinate level categories share parts, and (4) parts vary in perceived goodness. It was found that part terms proliferated in Ss' listings of attributes characterizing category members at the basic level, but were rarely listed at a general level. At a more specific level, fewer parts were listed, although more were judged to be true. Perceptual salience and functional significance both contributed to perceived part goodness. It is proposed that part configuration underlies the various empirical operations of perception, behavior, and communication that converge at the basic level. Part configuration underlies the perceptual measures because it determines the shapes of objects to a large degree. Parts underlie the behavioral tasks because most behavior is directed toward parts of objects. Labeling appears to follow the natural breaks of perception and behavior; consequently, part configuration also underlies communication measures. Because elements of more abstract taxonomies, such as scenes and events, can also be decomposed into parts, this analysis provides a bridge to organization in other domains of knowledge. (47 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)