definition of what nature is as applied
to substances alone. This definition comprises also the definition of
substance. For if the word nature signifies substance, when once we have
defined nature we have also settled the definition of substance. But if
we neglect incorporeal substances and confine the name nature to
corporeal substances so that they alone appear to possess the nature of
substance--which is the view of Aristotle and the adherents both of his
and various other schools--we shall define nature as those do who have
only allowed the word to be applied to bodies. Now, in accordance with
this view, the definition is as follows: "Nature is the principle of
movement properly inherent in and not accidentally attached to bodies."
I say "principle of movement" because every body has its proper
movement, fire moving upwards, the earth moving downwards. And what I
mean by "movement properly inherent and not accidentally attached" is
seen by the example of a wooden bed which is necessarily borne downward
and is not carried downward by accident. For it is drawn downward by
weight and heaviness because it is of wood, i.e. an earthly material.
For it falls down not because it is a bed, but because it is earth, that
is, because it is an accident of earth that it is a bed; hence we call
it wood in virtue of its nature, but bed in virtue of the art that
shaped it.

Nature has, further, another meaning according to which we speak of the
different nature of gold and silver, wishing thereby to point the
special property of things; this meaning of nature will be defined as
follows: "Nature is the specific difference that gives form to
anything." Thus, although nature is described or defined in all these
different ways, both Catholics and Nestorians firmly hold that there are
in Christ two natures of the kind laid down in our last definition, for
the same specific differences cannot apply to God and man.

II.

Sed de persona maxime dubitari potest, quaenam ei definitio possit aptari.
Si enim omnis habet natura personam, indissolubilis nodus est, quaenam
inter naturam personamque possit esse discretio; aut si non aequatur
persona naturae, sed infra terminum spatiumque naturae persona subsistit,
difficile dictu est ad quas usque naturas persona perueniat, id est quas
naturas conueniat habere personam, quas a personae uocabulo segregari. Nam
illud quidem manifestum es