inclination of habit is like that of nature
which tends to one thing. Now original sin, even in one man, inclines
to various and contrary sins. Therefore original sin is not one
habit; but several.

Obj. 3: Further, original sin infects every part of the soul. Now the
different parts of the soul are different subjects of sin, as shown
above (Q. 74). Since then one sin cannot be in different subjects, it
seems that original sin is not one but several.

_On the contrary,_ It is written (John 1:29): "Behold the Lamb of
God, behold Him Who taketh away the sin of the world": and the reason
for the employment of the singular is that the "sin of the world" is
original sin, as a gloss expounds this passage.

_I answer that,_ In one man there is one original sin. Two reasons
may be assigned for this. The first is on the part of the cause of
original sin. For it has been stated (Q. 81, A. 2), that the first
sin alone of our first parent was transmitted to his posterity.
Wherefore in one man original sin is one in number; and in all men,
it is one in proportion, i.e. in relation to its first principle. The
second reason may be taken from the very essence of original sin.
Because in every inordinate disposition, unity of species depends on
the cause, while the unity of number is derived from the subject. For
example, take bodily sickness: various species of sickness proceed
from different causes, e.g. from excessive heat or cold, or from a
lesion in the lung or liver; while one specific sickness in one man
will be one in number. Now the cause of this corrupt disposition that
is called original sin, is one only, viz. the privation of original
justice, removing the subjection of man's mind to God. Consequently
original sin is specifically one, and, in one man, can be only one in
number; while, in different men, it is one in species and in
proportion, but is numerically many.

Reply Obj. 1: The employment of the plural--"in sins"--may be
explained by the custom of the Divine Scriptures in the frequent use
of the plural for the singular, e.g. "They are dead that sought the
life of the child"; or by the fact that all actual sins virtually
pre-exist in original sin, as in a principle so that it is virtually
many; or by the fact of there being many deformities in the sin of
our first parent, viz. pride, disobedience, gluttony, and so forth;
or by several parts of the soul being infected by original sin.

Reply Obj. 2: Of itself and