Death is clearly a part of life—every day. And yet, the word defies simple definition, because there are so many aspects to death and so many perspectives. A 1913 edition of Webster's Dictionary defined death as "the cessation of all vital phenomena without capability of resuscitation, either in animals or plants." The current Concise Oxford Dictionary defines death both as "dying" (a process) and as "being dead" (a state). As intoned in the Old Testament of the Bible, "All flesh is as grass" (Isaiah 40:6–8). The body dies but in the religious and philosophical traditions of many observers, the soul or spirit lives on.
The Roman Catholic Church, for example, advances the thought that death is the "complete and final separation of the soul from the body." The church, however, concedes that diagnosing death is a subject for medicine, not the church. In the Zen Buddhist and Shintō religious traditions, mind and body are integrated, and followers have difficulty accepting the brain-death criteria that are now common in Western medical and legal circles. For some Orthodox Jews, Native Americans, Muslims, and fundamentalist Christians, as long as the heart is beating—even artificially—a person is still alive.
Advances in life-supporting technologies in the 1960s spawned the growth of medical ethics as a distinct field, and a new definition for physiological death was needed. For centuries death was indicated by the absence of a pulse or signs of breathing, but new technologies, including the respirator and heart–lung machine, made it possible for physicians to artificially maintain heart and lung function, blurring clear signs of an individual's death. In the United States many states have adopted legislation recognizing brain death—the loss of brain function, which controls breathing and heartbeat—as the certification of death. Canada, Australia, and most of the nations of Europe and Central and South America have broader definitions for death: either loss of all independent lung and heart function, or the permanent, irreversible loss of all brain function.
From a physiological standpoint, somatic death—the death of the organism as a whole—usually precedes the death of individual organs, cells, and parts of cells. The precise time of somatic death is sometimes difficult to determine because transient states, such as coma, fainting, and trance, can closely resemble the signs of death. Several changes in the body that occur after somatic death are used to determine the time of death and circumstances surrounding it. The cooling of the body, called algor mortis, is mainly influenced by the air temperature of the surrounding environment of the body. The stiffening of the skeletal muscles, called rigor mortis, begins from five to ten hours after death and ends in three or four days. The reddish-blue discoloration that occurs on the underside of the body, called livor mortis, is the result of blood settling in the body cavity. Shortly after death, blood clotting begins, along with autolysis, which is the death of the cells. The decomposition of the body that follows, called putrefaction, is the result of the action of enzymes and bacteria.