Chapter 36

54. There are also certain rules for a more copious kind of argument,
which is called eloquence, and these rules are not the less true that
they can be used for persuading men of what is false; but as they can
be used to enforce the truth as well, it is not the faculty itself that
is to be blamed, but the perversity of those who put it to a bad use.
Nor is it owing to an arrangement among men that the expression of
affection conciliates the hearer, or that a narrative, when it is short
and clear, is effective, and that variety arrests men’s attention
without wearying them. And it is the same with other directions of the
same kind, which, whether the cause in which they are used be true or
false, are themselves true just in so far as they are effective in
producing knowledge or belief, or in moving men’s minds to desire and
aversion. And men rather found out that these things are so, tha
arranged that they should be so.

Chapter 35

53. Again, the science of definition, of division, and of partition,
although it is frequently applied to falsities, is not itself false,
nor framed by man’s device, but is evolved from the reason of things.
For although poets have applied it to their fictions, and false
philosophers, or even heretics–that is, false Christians–to their
erroneous doctrines, that is no reason why it should be false, for
example, that neither in definition, nor in division, nor in partition,
is anything to be included that does not pertain to the matter in hand,
nor anything to be omitted that does. This is true, even though the
things to be defined or divided are not true. For even falsehood itself
is defined when we say that falsehood is the declaration of a state of
things which is not as we declare it to be; and this definition is
true, although falsehood itself cannot be true. We can also divide it,
saying that there are two kinds of falsehood, one in regard to things
that cannot be true at all, the other in regard to things that are not,
though it is possible they might be, true. For example, the man who
says that seven and three are eleven, says what cannot be true under
any circumstances; but he who says that it rained on the kalends of
January, although perhaps the fact is not so, says what possibly might
have been. The definition and division, therefore, of what is false may
be perfectly true, although what is false cannot, of course, itself be
true.

Chapter 34

52. Therefore it is one thing to know the laws of inference, and
another to know the truth of opinions. In the former case we learn what
is consequent, what is inconsequent, and what is incompatible. An
example of a consequent is, “If he is an orator, he is a man;” of an
inconsequent, “If he is a man, he is an orator;” of an incompatible,
“If he is a man, he is a quadruped.” In these instances we judge of the
connection. In regard to the truth of opinions, however, we must
consider propositions as they stand by themselves, and not in their
connection with one another; but when propositions that we are not sure
about are joined by a valid inference to propositions that are true and
certain, they themselves, too, necessarily become certain. Now some,
when they have ascertained the validity of the inference, plume
themselves as if this involved also the truth of the propositions.
Many, again, who hold the true opinions have an unfounded contempt for
themselves, because they are ignorant of the laws of inference; whereas
the man who knows that there is a resurrection of the dead is assuredly
better than the man who only knows that it follows that if there is no
resurrection of the dead, then is Christ not risen.

Chapter 33

51. In this passage, however, where the argument is about the
resurrection, both the law of the inference is valid, and the
conclusion arrived at is true. But in the case of false conclusions,
too, there is a validity of inference in some such way as the
following. Let us suppose some man to have admitted: If a snail is an
animal, it has a voice. This being admitted, then, when it has been
proved that the snail has no voice, it follows (since when the
consequent is proved false, the antecedent is also false) that the
snail is not an animal. Now this conclusion is false, but it is a true
and valid inference from the false admission. Thus, the truth of a
statement stands on its own merits; the validity of an inference
depends on the statement or the admission of the man with whom one is
arguing. And thus, as I said above, a false inference may be drawn by a
valid process of reasoning, in order that he whose error we wish to
correct may be sorry that he has admitted the antecedent, when he sees
that its logical consequences are utterly untenable. And hence it is
easy to understand that as the inferences may be valid where the
opinions are false, so the inferences may be unsound where the opinions
are true. For example, suppose that a man propounds the statement, “If
this man is just, he is good,” and we admit its truth. Then he adds,
“But he is not just;” and when we admit this too, he draws the
conclusion, “Therefore he is not good.” Now although every one of these
statements may be true, still the principle of the inference is
unsound. For it is not true that, as when the consequent is proved
false the antecedent is also false, so when the antecedent is proved
false the consequent is false. For the statement is true, “If he is an
orator, he is a man.” But if we add, “He is not an orator,” the
consequence does not follow, “He is not a man.”

Chapter 32

50. And yet the validity of logical sequences is not a thing devised by
men, but is observed and noted by them that they may be able to learn
and teach it; for it exists eternally in the reason of things, and has
its origin with God. For as the man who narrates the order of events
does not himself create that order; and as he who describes the
situations of places, or the natures of animals, or roots, or minerals,
does not describe arrangements of man; and as he who points out the
stars and their movements does not point out anything that he himself
or any other man has ordained;–in the same way, he who says, “When the
consequent is false, the antecedent must also be false,” says what is
most true; but he does not himself make it so, he only points out that
it is so. And it is upon this rule that the reasoning I have quoted
from the Apostle Paul proceeds. For the antecedent is, “There is no
resurrection of the dead,” the position taken up by those whose error
the apostle wished to overthrow. Next, from this antecedent, the
assertion, viz., that there is no resurrection of the dead, the
necessary consequence is, “Then Christ is not risen.” But this
consequence is false, for Christ has risen; therefore the antecedent is
also false. But the antecedent is, that there is no resurrection of the
dead. We conclude, therefore, that there is a resurrection of the dead.
Now all this is briefly expressed thus: If there is no resurrection of
the dead, then is Christ not risen; but Christ is risen, therefore
there is a resurrection of the dead. This rule, then, that when the
consequent is removed, the antecedent must also be removed, is not made
by man, but only pointed out by him. And this rule has reference to the
validity of the reasoning, not to the truth of the statements.

Chapter 31

48. There remain those branches of knowledge which pertain not to the
bodily senses, but to the intellect, among which the science of
reasoning and that of number are the chief. The science of reasoning is
of very great service in searching into and unravelling all sorts of
questions that come up in Scripture, only in the use of it we must
guard against the love of wrangling, and the childish vanity of
entrapping an adversary. For there are many of what are called
sophisms, inferences in reasoning that are false, and yet so close an
imitation of the true, as to deceive not only dull people, but clever
men too, when they are not on their guard. For example, one man lays
before another with whom he is talking, the proposition, “What I am,
you are not.” The other assents, for the proposition is in part true,
the one man being cunning and the other simple. Then the first speaker
adds: “I am a man;” and when the other has given his assent to this
also, the first draws his conclusion: “Then you are not a man.” Now at
this sort of ensnaring arguments, Scripture, as I judge, expresses
detestation in that place where it is said, “There is one that showeth
wisdom in words, and is hated;” although, indeed, a style of speech
which is not intended to entrap, but only aims at verbal ornamentation
more than is consistent with seriousness of purpose, is also called
sophistical.

49. There are also valid processes of reasoning which lead to false
conclusions, by following out to its logical consequences the error of
the man with whom one is arguing; and these conclusions are sometimes
drawn by a good and learned man, with the object of making the person
from whose error these consequences result, feel ashamed of them, and
of thus leading him to give up his error, when he finds that if he
wishes to retain his old opinion, he must of necessity also hold other
opinions which he condemns. For example, the apostle did not draw true
conclusions when he said, “Then is Christ not risen,” and again, “Then
is our preaching vain, and your faith is also vain;” and further on
drew other inferences which are all utterly false; for Christ has
risen, the preaching of those who declared this fact was not in vain,
nor was their faith in vain who had believed it. But all these false
inferences followed legitimately from the opinion of those who said
that there is no resurrection of the dead. These inferences, then,
being repudiated as false, it follows that since they would be true if
the dead rise not, there will be a resurrection of the dead. As, then,
valid conclusions may be drawn not only from true but from false
propositions, the laws of valid reasoning may easily be learnt in the
schools, outside the pale of the Church. But the truth of propositions
must be inquired into in the sacred books of the Church.