The soul of man is divided by him into three parts, answering
roughly to the charioteer and steeds of the Phaedrus, and to the
(Greek) of the Republic and Nicomachean Ethics. First, there is
the immortal nature of which the brain is the seat, and which is
akin to the soul of the universe. This alone thinks and knows and
is the ruler of the whole. Secondly, there is the higher mortal
soul which, though liable to perturbations of her own, takes the
side of reason against the lower appetites. The seat of this is
the heart, in which courage, anger, and all the nobler affections
are supposed to reside. There the veins all meet; it is their
centre or house of guard whence they carry the orders of the
thinking being to the extremities of his kingdom. There is also a
third or appetitive soul, which receives the commands of the
immortal part, not immediately but mediately, through the liver,
which reflects on its surface the admonitions and threats of the
reason.
The liver is imagined by Plato to be a smooth and bright
substance, having a store of sweetness and also of bitterness,
which reason freely uses in the execution of her mandates. In
this region, as ancient superstition told, were to be found
intimations of the future. But Plato is careful to observe that
although such knowledge is given to the inferior parts of man, it
requires to be interpreted by the superior. Reason, and not
enthusiasm, is the true guide of man; he is only inspired when he
is demented by some distemper or possession. The ancient saying,
that ‘only a man in his senses can judge of his own actions,’ is
approved by modern philosophy too. The same irony which appears
in Plato’s remark, that ‘the men of old time must surely have
known the gods who were their ancestors, and we should believe
them as custom requires,’ is also manifest in his account of
divination.
The appetitive soul is seated in the belly, and there imprisoned
like a wild beast, far away from the council chamber, as Plato
graphically calls the head, in order that the animal passions may
not interfere with the deliberations of reason. Though the soul
is said by him to be prior to the body, yet we cannot help seeing
that it is constructed on the model of the body—the threefold
division into the rational, passionate, and appetitive
corresponding to the head, heart and belly. The human soul
differs from the soul of the world in this respect, that it is
enveloped and finds its expression in matter, whereas the soul of
the world is not only enveloped or diffused in matter, but is the
element in which matter moves. The breath of man is within him,
but the air or aether of heaven is the element which surrounds
him and all things.