A number of great rabbis throughout the ages have accepted breathing and heartbeat as the parameters of death. However, we witness today that a clinically dead person, displaying neither breathing nor heartbeat, may be successfully revived. Does this state of affairs clash with the definition of death of our sages? I submit that the definition of death is primarily a matter of metaphysical, and not physical, change. It is contingent upon the soul leaving the body, as we find in the Mishnah (Ohalot 1:6): “A human [body] does not cause impurity until the soul departs.” No one can perceive the soul as it leaves the body; all that is available are signs of the event. In the time of the Talmudic sages, these signs were the cessation of both breathing and heartbeat. Today, however, via medical technology a clinically dead person can often be resuscitated. Such a case proves, albeit in ex post facto fashion, that the soul has not yet left the body. The definition of death has not changed; the signs have.
Another sign of death is decapitation. The same Mishnah quoted above also teaches: “If they were decapitated, even though they are convulsing, they are impure. [The movement] is similar to that of the [severed] tail of a lizard.” The Shulchan Aruch (Y.D., Laws of Mourning, 370) rules: “One whose neckbone and a majority of the adjacent flesh has been severed, one whose back has been split open as one does to a fish, even though he is still alive [i.e. he is moving] he is considered dead and is impure. But one who is on the verge of dying or one whose trachea and esophagus were cut… are not impure until their soul departs.” One might want to compare total brain death to severance of the neck or decapitation. Even though his heart is beating or he displays bodily movement, he is nevertheless considered dead. However, if his brain is not totally dead and his heart continues to beat, he is at this point considered alive halachically. Therefore, brain stem death cannot be associated with this Mishnah.
Decapitation, however, is not always a sure sign of the soul’s departure. The saintly dean of the Volozhin Yeshiva, Rabbi Naftali Tzvi Yehuda Berlin, states (Emek HaNetziv, p. 167): “There is a long-standing tradition, transmitted from one generation of rabbis to the next, that the soul of one who is killed by decapitation [i.e. a violent death] experiences difficulty in departing even if he is definitely dead. [Any movement, therefore, is merely a reflexive reaction.] But in the case under consideration, the person has died of natural causes. As long as there are any signs of life or movement, they represent a clear indication that the person has not yet expired.” Even if total brain death is accepted as equivalent to decapitation, and the person would therefore be considered dead even if his heart continues to beat, this would only apply if brain death occurred violently. In a situation in which total brain death proceeded gradually, the heartbeat would indeed be considered a sign of life.
Additionally, Tosefot Rid (Shabbat 136a) posits that an extended period of movement refutes the analogy to a severed tail of a lizard. In a circumstance of total brain death in which the heart nevertheless continues to beat of its own accord, and where the body is supplied with oxygen and nourishment so that the heart can continue to beat for days and weeks naturally, the patient is considered alive.
Our concern is the departure of the soul, an elusive metaphysical event that can only be seen through its effects and not directly. The signs of this departure are reflected in the laws of purity as described by our sages and interpreted throughout the millennia. While medical technology has changed, the definition of death remains constant and we have to turn to our mesorah, halachic sources and our gedolim to determine which signs today demonstrate that a person’s soul has left his body.