19. When things enter into the matter that plays the part of mother
to them, they neither hurt it, nor give it pleasure. Their blows
are not felt by matter; they direct their blows only against each
other, because the powers act upon their opposites, and not on their
substrates, unless indeed we consider the substrates as united to
the things they contain. Heat makes cold disappear,[92] as whiteness
affects blackness; or, if they mingle, they produce a new quality by
their mixture.[93] What is affected is the things that mingle, and
their being affected consists in ceasing to be what they were. Among
animate beings, it is the body that is affected by the alteration
of the qualities, and of the forces possessed. When the qualities
constitutive of these beings are destroyed, or when they combine, or
when they undergo some change contrary to their nature, the affections
relate to the body, as the perceptions do to the soul. The latter
indeed knows all the affections that produce a lively impression.
Matter, however, remains what it is; it could not be affected when it
ceases to contain heat or cold, since neither of these qualities is
either characteristic or foreign. The name that best characterizes
matter, therefore, is nurse or residence.[94] But in what sense could
matter, that begets nothing, be called "mother"? Those who call it
such consider a mother as playing the part of mere matter, towards her
child, merely receiving the germ, without contributing anything of
itself, because the body of the child owes its growth to nourishment.
If however the mother does contribute anything (to the formation of the
child) she then plays the part of form, and does not restrict herself
to the part of matter. Indeed, the form alone is fruitful, while the
"other nature" (that is, matter), is unfruitful.