ived from the special form of a thing. So in
the definition of "person," which means the singular in a determined
genus, it is more correct to use the term "nature" than "essence,"
because the latter is taken from being, which is most common.

Reply Obj. 5: The soul is a part of the human species; and so,
although it may exist in a separate state, yet since it ever retains
its nature of unibility, it cannot be called an individual substance,
which is the hypostasis or first substance, as neither can the hand
nor any other part of man; thus neither the definition nor the name
of person belongs to it.
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SECOND ARTICLE [I, Q. 29, Art. 2]

Whether "Person" Is the Same As Hypostasis, Subsistence, and Essence?

Objection 1: It would seem that "person" is the same as "hypostasis,"
"subsistence," and "essence." For Boethius says (De Duab. Nat.) that
"the Greeks called the individual substance of the rational nature by
the name hypostasis." But this with us signifies "person." Therefore
"person" is altogether the same as "hypostasis."

Obj. 2: Further, as we say there are three persons in God, so we say
there are three subsistences in God; which implies that "person" and
"subsistence" have the same meaning. Therefore "person" and
"subsistence" mean the same.

Obj. 3: Further, Boethius says (Com. Praed.) that the Greek _ousia,_
which means essence, signifies a being composed of matter and form.
Now that which is composed of matter and form is the individual
substance called "hypostasis" and "person." Therefore all the
aforesaid names seem to have the same meaning.

Obj. 4: _On the contrary,_ Boethius says (De Duab. Nat.) that genera
and species only subsist; whereas individuals are not only
subsistent, but also substand. But subsistences are so called from
subsisting, as substance or hypostasis is so called from substanding.
Therefore, since genera and species are not hypostases or persons,
these are not the same as subsistences.

Obj. 5: Further, Boethius says (Com. Praed.) that matter is called
hypostasis, and form is called _ousiosis_--that is, subsistence. But
neither form nor matter can be called person. Therefore person
differs from the others.

_I answer that,_ According to the Philosopher (Metaph. v), substance
is twofold. In one sense it means the quiddity of a thing, signified
by its definition, and thus we say that the definition means the
substance of a thing; in which sense substanc