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“we should shape our opinions according to the pattern
of nature.”
9
Human nature itself is the source of what is
common to all human beings. Sin is derived through origin
not because concupiscence in the act of generation infects
the soul but because origin involves the human generation
in which human nature is transmitted. Men receive their
nature from Adam. Human nature is
this sort
of human
nature, and not some other sort, because of its origins in
the first parents. As an act of nature, generation itself is
the sufficient explanation of the unity of the concrete hu-
man race with Adam. For Aquinas, the concupiscence that
may be involved in the act of generation is not some sort
of sinful lust but simply the absence in nature of an order
that would have prevailed in the state of original justice.
Aquinas adheres strictly to this path in order to explain
the voluntariness of original sin and thus its truly sinful
nature. “So too the disorder which is in an individual
man, a descendant of Adam, is not voluntary by reason of
personal will, but by reason of the will of the first parent,
who through a generative impulse [
motione generationis
]
exerts influence upon all who descend from him by way of
origin, even as the will of the soul moves bodily members
to their various activities.”
10
Aquinas rejects explanations
that suggest that all men
ratify
Adam’s personal sin, or that
they
acted in
Adam, or were
represented by
Adam—theo-
ries without foundation in divine revelation. Original sin
is voluntary, not by the will of the individual agent, but by
the will of Adam. All men can be considered as one man
because all are one in that the nature they share is de-
rived from one source. Adam’s causality is limited, just as
the “sin” in original sin is analogous. “Adam’s influence is
9 ST 1a. 101, 1
10 ST 1a2ae. 81, 1