In the soul weakness does not derive from an excess of density or
rarefaction of leanness or stoutness, nor of any sickness such as
fever. It must be met in souls which are either entirely separated from
matter, or in those joined to matter, or in both simultaneously. Now,
as it does not occur in souls separated from matter, which are entirely
pure, and "winged,"[193] and which, as perfect, carry out their
functions without any obstacle; it remains, that this weakness occurs
in fallen souls, which are neither pure nor purified. For them weakness
consists not in the privation of anything, but in the presence of
something alien, just as, for instance, weakness of the body consists
in the presence of slime or bile. We shall, therefore, be able to
understand clearly the weakness of the soul by ferreting out the cause
of the "fall" of the soul.