Lieh Tzu also called Lieh Yu-K’ou (440?–360? . .), Chinese Taoist philosopher whose name serves as the title of a work of disputed date. The Lieh Tzu, parts (perhaps most) of which were written as late as the third or fourth century A.D., is primarily a Taoist work but contains one chapter reflecting ideas associated with Yang Chu. However, whereas the original teachings of Yang Chu emphasized one’s duty to preserve bodily integrity, health, and longevity, a task that may require exercise and discipline, the Yang Chu chapter advocates hedonism as the means to nourish life. The primary Taoist teaching of the Lieh Tzu is that destiny trumps will, fate conquers effort. R.P.P. & R.T.A. life, the characteristic property of living substances or things; it is associated with either a capacity for mental activities such as perception and thought (mental life) or physical activities such as absorption, excretion, metabolism, synthesis, and reproduction (physical life). Biological or carbon-based life is a natural kind of physical life that essentially involves a highly complex, selfregulating system of carbon-based macromolecules and water molecules. Silicon-based life is wholly speculative natural kind of physical life that essentially involves a highly complex, selfregulating system of silicon-based macromolecules. This kind of life might be possible, since at high temperatures silicon forms macromolecules with chemical properties somewhat similar to those of carbon-based macromolecules. Living organisms have a high degree of functional organization, with a regulating or controlling master part, e.g., a dog’s nervous system, or the DNA or nucleus of a single-celled organism. Mental life is usually thought to be dependent or supervenient upon physical life, but some philosophers have argued for the possibility at least of purely spiritual mental life, i.e., souls. The above characterization of biological life appropriately implies that viruses are not living things, since they lack the characteristic activities of living things, with the exception of an attenuated form of reproduction. See also ARTIFICIAL LIFE, ORGANIS. J.Ho. & G.Ro.