FIRST ARTICLE [I-II, Q. 76, Art. 1]

Whether Ignorance Can Be a Cause of Sin?

Objection 1: It would seem that ignorance cannot be a cause of sin:

because a non-being is not the cause of anything. Now ignorance is a

non-being, since it is a privation of knowledge. Therefore ignorance

is not a cause of sin.

Obj. 2: Further, causes of sin should be reckoned in respect of sin

being a _turning to_ something, as was stated above (Q. 75, A. 1).

Now ignorance seems to savor of _turning away_ from something.

Therefore it should not be reckoned a cause of sin.

Obj. 3: Further, every sin is seated in the will. Now the will does

not turn to that which is not known, because its object is the good

apprehended. Therefore ignorance cannot be a cause of sin.

_On the contrary,_ Augustine says (De Nat. et Grat. lxvii) "that some

sin through ignorance."

_I answer that,_ According to the Philosopher (Phys. viii, 27) a

moving cause is twofold, direct and indirect. A direct cause is one

that moves by its own power, as the generator is the moving cause of

heavy and light things. An indirect cause, is either one that removes

an impediment, or the removal itself of an impediment: and it is in

this way that ignorance can be the cause of a sinful act; because it

is a privation of knowledge perfecting the reason that forbids the

act of sin, in so far as it directs human acts.

Now we must observe that the reason directs human acts in accordance

with a twofold knowledge, universal and particular: because in

conferring about what is to be done, it employs a syllogism, the

conclusion of which is an act of judgment, or of choice, or an

operation. Now actions are about singulars: wherefore the conclusion

of a practical syllogism is a singular proposition. But a singular

proposition does not follow from a universal proposition, except

through the medium of a particular proposition: thus a man is

restrained from an act of parricide, by the knowledge that it is

wrong to kill one's father, and that this man is his father. Hence

ignorance about either of these two propositions, viz. of the

universal principle which is a rule of reason, or of the particular

circumstance, could cause an act of parricide. Hence it is clear that

not every kind of ignorance is the cause of a sin, but that alone

which removes the knowledge which would prevent the sinful act.

Consequently if a man's will be so disposed that he would not be

restrained from the act of parricide, even though he recognized his

father, his ignorance about his father is not the cause of his

committing the sin, but is concomitant with the sin: wherefore such a

man sins, not "through ignorance" but "in ignorance," as the

Philosopher states (Ethic. iii, 1).

Reply Obj. 1: Non-being cannot be the direct cause of anything: but

it can be an accidental cause, as being the removal of an impediment.

Reply Obj. 2: As knowledge, which is removed by ignorance, regards

sin as turning towards something, so too, ignorance of this respect

of a sin is the cause of that sin, as removing its impediment.

Reply Obj. 3: The will cannot turn to that which is absolutely

unknown: but if something be known in one respect, and unknown in

another, the will can will it. It is thus that ignorance is the cause

of sin: for instance, when a man knows that what he is killing is a

man, but not that it is his own father; or when one knows that a

certain act is pleasurable, but not that it is a sin.

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Summa Theologica, Part I-II (Pars Prima Secundae) From the Complete American Edition · 第 500 / 746 题