Human Dignity and Bioethics

The Mystery of the Human Soul | 69
combination of body and soul, which are not entirely distinct from
each other because they interact on a regular basis. The body clearly
exists as a substance because it differentiates one individual human
being from another. But the body’s shape is more than the sum of
its parts because it moves together on its own power as an integral
whole, requiring a form united with matter. This is the first meaning
of “soul”: the self-moving power of a body with form that functions
as a unified whole.
In this sense, all animals are a union of body and soul because
they move on their own power as integral wholes; and this is precisely
Aristotle’s point in his classic work, On the Soul. 14 His thesis is that
“the soul is the first principle of animal life”—meaning, the soul is
the cause of life in living beings. For Aristotle, life is a kind of mystery
because living beings have bodies that move on their own and
this implies the intangible power of “soul” (anima in Latin; psyche in
Greek). The puzzle is that the soul is not the same as the body, yet it
is also not separate from the body: “the soul does not exist without a
body and yet is not itself a kind of body.” Aristotle uses a variety of
expressions to capture this relation: “the soul is the actuality of the
body” and “the soul exists in a body” and “the product of the two is
an ensouled thing.” Aristotle’s expressions are attempts to describe
the unity of matter and form in a being whose body seems lifeless
without an immaterial cause that gives it motion and function. In
this view, the soul actualizes the potential of the body to do its proper
work.
What surprises the reader of Aristotle is the claim that all living
beings have “souls”—there are plant souls, animal souls, and human
souls. While shocking at first, Aristotle’s idea follows common sense
in distinguishing living beings by three different capacities: (1) selfmotion,
(2) sense perception, and (3) thinking. All living things are
distinguished from non-living things by the power of self-motion—
either by growing (including feeding and reproducing) or by moving
from place to place (local motion). Plants are self-moving in the sense
of feeding, growing, and reproducing; hence, they have “plant souls.”
Animals have self-motion and sense perception, and even some capacity
for desiring and wishing that seems to involve “imagination,” if not
intellectual activity. Hence, they have “animal souls.” Human beings
have “human souls” because their souls include all three powers—self-