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ON CHRISTIAN DOCTRINE
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by St Augustine of Hippo |
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Ch 31. Use of dialectics. Of fallacies |
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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.
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Ch 32. Valid logical sequence is not devised but only
observed by man |
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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.
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Ch 33. False inferences may be drawn from valid
seasonings, and vice versa |
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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."
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Ch 34. It is one thing to know
the laws of inference, another to know the truth of opinions |
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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.
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Ch 35. The science of definition is not false, though
it may be applied to falsities |
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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.
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Ch 36. The rules of eloquence are true, though
sometimes used to persuade men of what is false |
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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,
than arranged that they should be so. |
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