I turned to [Aristotle's] De Anima (On Soul), expecting to get help with understanding the difference between a living human being and its corpse, re… - Leon Kass

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I turned to [Aristotle's] De Anima (On Soul), expecting to get help with understanding the difference between a living human being and its corpse, relevant for the difficult task of determining whether some persons on a respirator are alive or dead. I discovered to my amazement that Aristotle has almost no interest in the difference between the living and the dead. Instead, one learns most about life and soul not, as we moderns might suspect, from the boundary conditions when an organism comes into being or passes away, but rather when the organism is at its peak, its capacious body actively at work in energetic relation to—that is, in "souling"—the world: in the activities of sensing, imagining, desiring, moving, and thinking. Even more surprising, in place of our dualistic ideas of soul as either a "ghost in the machine," invoked by some in order to save the notion of free will, or as a separate immortal entity that departs the body at the time of death, invoked by others to address the disturbing fact of apparent personal extinction, Aristotle offers a powerful and still defensible holistic idea of soul as the empowered and empowering "form of a naturally organic body." "Soul" names the unified powers of aliveness, awareness, action, and appetite that living beings all manifest.
This is not mysticism or superstition, but biological fact, albeit one that, against current prejudice, recognizes the difference between mere material and its empowering form. Consider, for example, the eye. The eye's power of sight, though it "resides in" and is inseparable from material, is not itself material. Its light-absorbing chemicals do not see the light they absorb. Like any organ, the eye has extension, takes up space, can be touched and grasped by the hand. But neither the power of the eye — sight — nor sight's activity — seeing — is extended, ­touchable, ­corporeal. Sight and seeing are powers and activities of soul, relying on the underlying materials but not reducible to them. Moreover, sight and seeing are not knowable through our objectified science, but only through lived experience. A blind neuroscientist could give precise quantitative details regarding electrical discharges in the eye produced by the stimulus of light, and a blind craftsman could with instruction fashion a good material model of the eye; but sight and seeing can be known only by one who sees.