Logic, Dialectic, and Rhetoric go together, because they make up the whole
of a _technic of reason_, and under this title they ought also to be
taught—Logic as the technic of our own thinking, Dialectic of disputing
with others, and Rhetoric of speaking to many (_concionatio_); thus
corresponding to the singular, dual, and plural, and to the monologue, the
dialogue, and the panegyric.
Under Dialectic I understand, in agreement with Aristotle (_Metaph._, iii.
2, and _Analyt. Post._, i. 11), the art of conversation directed to the
mutual investigation of truth, especially philosophical truth. But a
conversation of this kind necessarily passes more or less into
controversy; therefore dialectic may also be explained as the art of
disputation. We have examples and patterns of dialectic in the Platonic
dialogues; but for the special theory of it, thus for the technical rules
of disputation, eristics, very little has hitherto been accomplished. I
have worked out an attempt of the kind, and given an example of it, in the
second volume of the “Parerga,” therefore I shall pass over the exposition
of this science altogether here.
In Rhetoric the rhetorical figures are very much what the syllogistic
figures are in Logic; at all events they are worth considering. In
Aristotle’s time they seem to have not yet become the object of
theoretical investigation, for he does not treat of them in any of his
rhetorics, and in this reference we are referred to Rutilius Lupus, the
epitomiser of a later Gorgias.
All the three sciences have this in common, that without having learned
them we follow their rules, which indeed are themselves first abstracted
from this natural employment of them. Therefore, although they are of
great theoretical interest, they are of little practical use; partly
because, though they certainly give the rule, they do not give the case of
its application; partly because in practice there is generally no time to
recollect the rules. Thus they teach only what every one already knows and
practises of his own accord; but yet the abstract knowledge of this is
interesting and important. Logic will not easily have a practical value,
at least for our own thinking. For the errors of our own reasoning
scarcely ever lie in the inferences nor otherwise in the form, but in the
judgments, thus in the matter of thought. In controversy, on the other
hand, we can sometimes derive some practical use from logic, by taking the
more or less intentionally deceptive argument of our opponent, which he
advances under the garb and cover of continuous speech, and referring it
to the strict form of regular syllogisms, and thus convicting it of
logical errors; for example, simple conversion of universal affirmative
judgments, syllogisms with four terms, inferences from the consequent to
the reason, syllogisms in the second figure with merely affirmative
premisses, and many such.
It seems to me that the doctrine of the laws of thought might be
simplified if we were only to set up two, the law of excluded middle and
that of sufficient reason. The former thus: “Every predicate can either be
affirmed or denied of every subject.” Here it is already contained in the
“either, or” that both cannot occur at once, and consequently just what is
expressed by the laws of identity and contradiction. Thus these would be
added as corollaries of that principle which really says that every two
concept-spheres must be thought either as united or as separated, but
never as both at once; and therefore, even although words are brought
together which express the latter, these words assert a process of thought
which cannot be carried out. The consciousness of this infeasibility is
the feeling of contradiction. The second law of thought, the principle of
sufficient reason, would affirm that the above attributing or denying must
be determined by something different from the judgment itself, which may
be a (pure or empirical) perception, or merely another judgment. This
other and different thing is then called the ground or reason of the
judgment. So far as a judgment satisfies the first law of thought, it is
thinkable; so far as it satisfies the second, it is true, or at least in
the case in which the ground of a judgment is only another judgment it is
logically or formally true. But, finally, material or absolute truth is
always the relation between a judgment and a perception, thus between the
abstract and the concrete or perceptible idea. This is either an immediate
relation or it is brought about by means of other judgments, _i.e._,
through other abstract ideas. From this it is easy to see that one truth
can never overthrow another, but all must ultimately agree; because in the
concrete or perceptible, which is their common foundation, no
contradiction is possible. Therefore no truth has anything to fear from
other truths. Illusion and error have to fear every truth, because through
the logical connection of all truths even the most distant must some time
strike its blow at every error. This second law of thought is therefore
the connecting link between logic and what is no longer logic, but the
matter of thought. Consequently the agreement of the conceptions, thus of
the abstract idea with what is given in the perceptible idea, is, on the
side of the object _truth_, and on the side of the subject _knowledge_.
To express the union or separation of two concept-spheres referred to
above is the work of the copula, “is—is not.” Through this every verb can
be expressed by means of its participle. Therefore all judging consists in
the use of a verb, and _vice versâ_. Accordingly the significance of the
copula is that the predicate is to be thought in the subject, nothing
more. Now, consider what the content of the infinitive of the copula “to
be” amounts to. But this is a principal theme of the professors of
philosophy of the present time. However, we must not be too strict with
them; most of them wish to express by it nothing but material things, the
corporeal world, to which, as perfectly innocent realists at the bottom of
their hearts, they attribute the highest reality. To speak, however, of
the bodies so directly appears to them too vulgar; and therefore they say
“being,” which they think sounds better, and think in connection with it
the tables and chairs standing before them.
“For, because, why, therefore, thus, since, although, indeed, yet, but,
if, then, either, or,” and more like these, are properly _logical
particles_, for their only end is to express the form of the thought
processes. They are therefore a valuable possession of a language, and do
not belong to all in equal numbers. Thus “_zwar_” (the contracted “_es ist
wahr_”) seems to belong exclusively to the German language. It is always
connected with an “_aber_” which follows or is added in thought, as “if”
is connected with “then.”
The logical rule that, as regards quantity, singular judgments, that is,
judgments which have a singular conception (_notio singularis_) for their
subject, are to be treated as _universal judgments_, depends upon the
circumstance that they are in fact universal judgments, which have merely
the peculiarity that their subject is a conception which can only be
supported by a single real object, and therefore only contains a single
real object under it; as when the conception is denoted by a proper name.
This, however, has really only to be considered when we proceed from the
abstract idea to the concrete or perceptible, thus seek to realise the
conceptions. In thinking itself, in operating with judgments, this makes
no difference, simply because between singular and universal conceptions
there is no logical difference. “Immanuel Kant” signifies logically,
“_all_ Immanuel Kant.” Accordingly the quantity of judgments is really
only of two kinds—universal and particular. An _individual idea_ cannot be
the subject of a judgment, because it is not an abstraction, it is not
something thought, but something perceived. Every conception, on the other
hand, is essentially universal, and every judgment must have a
_conception_ as its subject.
The difference between _particular judgments_ (_propositiones
particulares_) and _universal judgments_ often depends merely on the
external and contingent circumstance that the language has no word to
express by itself the part that is here to be separated from the general
conception which forms the subject of such a judgment. If there were such
a word many a particular judgment would be universal. For example, the
particular judgment, “Some trees bear gall-nuts,” becomes a universal
judgment, because for this part of the conception, “tree,” we have a
special word, “All oaks bear gall-nuts.” In the same way is the judgment,
“Some men are black,” related to the judgment, “All negroes are black.” Or
else this difference depends upon the fact that in the mind of him who
judges the conception which he makes the subject of the particular
judgment has not become clearly separated from the general conception as a
part of which he defines it; otherwise he could have expressed a universal
instead of a particular judgment. For example, instead of the judgment,
“Some ruminants have upper incisors,” this, “All unhorned ruminants have
upper incisors.”
The _hypothetical and disjunctive judgments_ are assertions as to the
relation of two (in the case of the disjunctive judgment even several)
categorical judgments to each other. The _hypothetical judgment_ asserts
that the truth of the second of the two categorical judgments here linked
together depends upon the truth of the first, and the falseness of the
first depends upon the falseness of the second; thus that these two
propositions stand in direct community as regards truth and falseness. The
_disjunctive judgment_, on the other hand, asserts that upon the truth of
one of the categorical judgments here linked together depends the
falseness of the others, and conversely; thus that these propositions are
in conflict as regards truth and falseness. The _question_ is a judgment,
one of whose three parts is left open: thus either the copula, “Is Caius a
Roman—or not?” or the predicate, “Is Caius a Roman—or something else?” or
the subject, “Is Caius a Roman—or is it some one else who is a Roman?” The
place of the conception which is left open may also remain quite empty;
for example, “What is Caius?”—“Who is a Roman?”
The επαγωγη, inductio, is with Aristotle the opposite of the απαγωγη. The
latter proves a proposition to be false by showing that what would follow
from it is not true; thus by the _instantia in contrarium_. The επαγωγη,
on the other hand, proves the truth of a proposition by showing that what
would follow from it is true. Thus it leads by means of examples to our
accepting something while the απαγωγη leads to our rejecting it. Therefore
the επαγωγη, or induction, is an inference from the consequents to the
reason, and indeed _modo ponente_; for from many cases it establishes the
rule, from which these cases then in their turn follow. On this account it
is never perfectly certain, but at the most arrives at very great
probability. However, this _formal_ uncertainty may yet leave room for
_material_ certainty through the number of the sequences observed; in the
same way as in mathematics the irrational relations are brought infinitely
near to rationality by means of decimal fractions. The απαγωγη, on the
contrary, is primarily an inference from the reason to the consequents,
though it is afterwards carried out _modo tollente_, in that it proves the
non-existence of a necessary consequent, and thereby destroys the truth of
the assumed reason. On this account it is always perfectly certain, and
accomplishes more by a single example _in contrarium_ than the induction
does by innumerable examples in favour of the proposition propounded. So
much easier is it to refute than to prove, to overthrow than to establish.