12. (17). (The Stoics), indeed, claim that every soul is perishable.
In this case, everything should long since have been destroyed. Others
might say that our soul were mortal, while the universal Soul were
immortal. On them, however, is the burden of proof of a difference
between the individual and universal souls. Both of them, indeed,
are a principle of movement; both live by themselves; both grasp
the same object by the same faculty, either by thinking the things
contained in heaven, or by considering the nature ("being") of each
being, ascending unto the first principle. Since our soul thinks
absolute essences either by the notions she finds within herself, or by
reminiscence, she evidently is prior to the body. Possessing knowledge
of eternal entities, she herself must be eternal. All that dissolves,
existing only by its compositeness, can naturally dissolve in the
same manner that it became composite. But the soul is a single, simple
actualization, whose essence is life; not in this manner therefore
can the soul perish. Neither could the soul perish by division into
a number of parts; for, as we have shown, the soul is neither a mass
nor a quantity. As little could the soul perish by alteration; for
when alteration destroys anything, it may remove its form, but leaves
its matter; alteration, therefore, is a characteristic of something
composite. Consequently as the soul cannot perish in any of these ways,
she is imperishable.