LOGIC OF THE STOICS.
[A. General remarks.]
[(1) Field of logic.]
Under the head of Logic, in the Stoic use of the term after the time of
Chrysippus, a number of intellectual enquiries are included which would
not now be considered to belong to philosophy at all. One common
element, however, characterised them all—they all referred to the
formal conditions of thought and expression. Logic was primarily
divided into two parts, sharply marked off from each other, roughly
described as the art of speaking continuously and the art of
conversing. The former is known as Rhetoric, the latter as Dialectic.
[112] To these two was added, as a third part, the doctrine of a
standard of truth, or the theory of knowledge; and, according to some
authorities, [113] a fourth part, consisting of enquiries into the
formation of conceptions. By others, these enquiries were regarded as
the third main division, the theory of knowledge being included under
dialectic. [114] By rhetoric, however, little else was meant than a
collection of artificial rules, of no philosophical value; [115] and
dialectic was in great measure occupied with enquiries referring to
precision of expression. Dialectic is defined to be the science or art
of speaking well; [116] and since speaking well consists in saying what
is becoming and true, [117] dialectic is used to express the knowledge
of what is true or false, or what is neither one nor the other, [118]
correctness of expression being considered inseparable [(2) Words and
thoughts.] from correctness of thought. Words and thoughts are,
according to this view, the very same things regarded under different
aspects. The same idea (λόγος), which is a thought as long as it
resides within the breast, is a word as soon as it comes forth. [119]
Accordingly, dialectic consists of two main divisions, treating
respectively of utterance and the thing uttered, thoughts and words.
[120] Both divisions, again, have several subdivisions, [121] which are
only imperfectly known to us. [122] Under the science of utterance,
which was generally placed before the science of things uttered, [123]
are included, not only instruction as to sounds and speech, but also
the theories of poetry and music, these arts being ranked under the
head of the voice and of sound on purely external considerations. [124]
What is known of the teaching of the Stoics on these subjects,
consisting, as it does, of a mass of definitions, differences, and
divisions, has so little philosophical value, that it need not detain
attention longer. [125] Two parts only of the Stoic logic possess any
real interest—the theory of knowledge, and that part of dialectic which
treats of ideas, and which in the main agrees with our formal logic.
[B. Theory of knowledge.]
[(1) General character of this theory.]
The Stoic theory of knowledge turns about the enquiry for a criterion
or standard by which what is true in notions may be distinguished from
what is false. Since every kind of knowledge, no matter what be its
object, must be tested by this standard, it follows that the standard
cannot be sought in the subject-matter of notions, but, on the
contrary, in their form. The enquiry after a standard becomes therefore
identical with another—the enquiry as to what kind of notions supply a
knowledge that may be depended upon, or what activity of the power of
forming conceptions carries with it a pledge of its own truth. It is
impossible to answer these questions without investigating the origin,
the various kinds, and the value and importance of notions. Hence the
problem proposed to the Stoics is reduced to seeking by an analysis of
notions to obtain a universally valid standard by which their truth may
be tested.
Whether this enquiry was pursued by the older Stoics in all its
comprehensiveness is a point on which we have no information. Boëthus,
whose views on this subject were attacked by Chrysippus, had assumed
the existence of several standards, such as Reason, Perception, Desire,
Knowledge. Others, in the vaguest manner, had spoken of Right Reason
(ὀρθὸς λόγος) as being the standard of truth. [126] Hence it may be
inferred that before the time of Chrysippus the Stoics had no
distinctly developed theory of knowledge. Nevertheless there are
expressions of Zeno and Cleanthes still extant which prove that the
essential parts of the later theory were already held by these
philosophers, [127] although it is no doubt true that it first received
that scientific form in which alone it is known to us at the hands of
Chrysippus.
[(2) Prominent points in the theory of knowledge.]
The character of this theory of knowledge appears mainly in three
particulars:—(1) In the importance attached by the Stoics to the
impressions of the senses. This feature they inherited from the Cynics
and shared with the Epicureans. (2) In the exaltation of expression
into a conception—a trait distinguishing this from either of the two
other contemporary Schools. (3) In the practical turn given to the
question of a criterion or standard of truth. We proceed to the
expansion of this theory in detail.
[(a) Perceptions the result of impressions from without.]
The origin of all perceptions (φαντασίαι) may be referred to the action
of some object (φανταστὸν) on the soul, [128] the soul at birth
resembling a blank page, and only receiving definite features by
experience from without. [129] By the elder Stoics, this action of
objects on the soul was regarded as grossly material, Zeno defining a
perception to be an impression (τύπωσις) made on the soul, [130] and
Cleanthes took this definition so literally as to compare the
impression on the soul to the impression made by a seal on wax. [131]
Being himself a very exact pupil of Zeno, Cleanthes probably rendered
the views of Zeno correctly in this comparison. The difficulties of
this view were recognised by Chrysippus, who accordingly defined a
perception to be the change (ἑτεροίωσις) produced in the soul by an
object, or, more accurately, the change produced thereby in the ruling
part of the soul; [132] and whereas his predecessors had only
considered sensible things to be objects, he included among objects
conditions and activities of the mind. [133] The mode, however, in
which the change was produced in the soul did not further engage his
attention.
[(b) Conceptions formed from perceptions.]
It follows, as a necessary corollary from this view, that the Stoics
regarded sensation as the only source of all perceptions: the soul is a
blank leaf, sensation is the hand which fills it with writing. But this
is not all. Perceptions give rise to memory, repeated acts of memory to
experience, [134] and conclusions based on experience suggest
conceptions which go beyond the sphere of direct sensation. These
conclusions rest either upon the comparison, or upon the combination of
perceptions, or else upon analogy; [135] some add, upon transposition
and contrast. [136] The formation of conceptions by means of these
agencies sometimes takes place methodically and artificially, at other
times naturally and spontaneously. [137] [(α) Κοιναὶ ἔννοιαι formed
naturally.] In the latter way are formed the primary conceptions,
προλήψεις or κοιναὶ ἔννοιαι, which were regarded by the Stoics as the
natural types of truth and virtue, and as the distinctive possession of
rational beings. [138] To judge by many expressions, it might seem that
by primary conceptions, or κοιναὶ ἔννοιαι, [139] innate ideas were
meant; but this view would be opposed to the whole character and
connection of the system. In reality, these primary conceptions, or
κοιναὶ ἔννοιαι, are only those conceptions which, by reason of the
nature of thought, can be equally deduced by all men from experience;
even the highest ideas, those of good and evil, having no other origin.
[140] The artificial formation of conceptions gives rise to knowledge,
which is defined by the Stoics to be a fixed and immovable conception,
or system of such conceptions. [141] Persistently maintaining, [(β)
Knowledge formed artificially.] on the one hand, that knowledge is a
system of artificial conceptions, impossible without a logical process,
they must, on the other hand, have felt it imperative from this
platform that knowledge should agree in its results with primary
conceptions, [142] agreement with nature being in every department
their watchword. For them it was as natural to derive support for their
system from a supposed agreement with nature, as it was easy for their
opponents to show that this agreement with nature was imaginary, and
that many of their assertions were wholly opposed to general opinions.
[143]
[(c) Relation of perceptions and conceptions.]
Perceptions, and the conclusions based upon them, [144] being thus,
according to the Stoics, the two sources of all notions, the further
question arises, How are these two sources related to each other? It
might have been expected that only perceptions would be stated to be
originally and absolutely true, since all general conceptions are based
on them. Nevertheless, the Stoics are far from saying so. Absolute
certainty of conviction they allow only to knowledge, and therefore
declare that the truth of the perceptions of the senses depends on
their relation to thought. [145] Truth and error do not belong to
disconnected notions, but to notions combined in the form of a
judgment, and a judgment is produced by an effort of thought. Hence
sensations, taken alone, are the source of no knowledge, knowledge
first arising when the activity of the understanding is allied to
sensation. [146] Or, starting from the relation of thought to its
object, since like can only be known by like according to the
well-known adage, the rational element in the universe can only be
known by the rational element in man. [147] But again, the
understanding has no other material to work upon but that supplied by
sensation, and general conceptions are only obtained from sensation by
conclusions. The mind, therefore, has the capacity of formally working
up the material supplied by the senses, but to this material it is
limited. Still, it can progress from perceptions to notions not
immediately given in sensation, such as the conceptions of what is good
and of God. And since, according to the Stoic teaching, material
objects only possess reality, the same vague inconsistency may be
observed in their teaching as has been noticed in Aristotle
[148]—reality attaching to individuals, truth to general notions. This
inconsistency, however, is more marked in their case than in that of
Aristotle, because the Stoics so far adhere to the Cynic nominalism
[149] as to assert that no reality attaches to thought. [150] Such an
assertion makes it all the more difficult to understand how greater
truth can be attributed to thought, unreal as it is said to be, than to
sensations of real and material objects. Do we then ask in what the
peculiar character of thought consists, the Stoics, following
Aristotle, reply that in thought the idea of universality is added to
that which presents itself in sensation as a particular. [151] More
importance was attached by them to another point—the greater certainty
which belongs to thought than to sensation. All the definitions given
above point to the immovable strength of conviction as the distinctive
feature of knowledge; [152] and of like import is the language
attributed to Zeno, [153] comparing simple sensation with an extended
finger, assent, as being the first activity of the power of judgment,
with a closed hand, conception with the fist, and knowledge with one
fist firmly grasped by the other. According to this view, the whole
difference between the four processes is one of degree, and depends on
the greater or less strength of conviction, on the mental exertion and
tension. [154] It is not an absolute difference in kind, but a relative
difference, a gradual shading off of one into the other.
[(d) The standard of truth.]
[(α) Practical need of such a standard.]
From these considerations it follows that in the last resort only a
relative distinction is left whereby the truth of notions may be
tested. Even the general argument for the possibility of knowledge
starts with the Stoics by practically taking something for granted.
Without failing to urge intellectual objections—and often most
pertinent ones [155]—against Scepticism, as was indeed natural,
particularly since the time of Chrysippus, [156] the Stoics
nevertheless specially took up their stand on one point, which was
this, that, unless the knowledge of truth were possible, it would be
impossible to act on fixed principles and convictions. [157] Thus, as a
last bulwark against doubt, practical needs are appealed to.
[(β) Irresistible perceptions the standard of truth.]
The same result is obtained from a special enquiry into the nature of
the standard of truth. If the question is asked, How are true
perceptions distinguished from false ones? the immediate reply given by
the Stoics is, that a true perception is one which represents a real
object as it really is. [158] You are no further with this answer, and
the question has again to be asked, How may it be known that a
perception faithfully represents a reality? The Stoics can only reply
by pointing to a relative, but not to an absolute, test—the degree of
strength with which certain perceptions force themselves on our notice.
By itself a perception does not necessarily carry conviction or assent
(συγκατάθεσις); for there can be no assent until the faculty of
judgment is directed towards the perception, either for the purpose of
allowing or of rejecting it, truth and error residing in judgment.
Assent therefore, generally speaking, rests with us, as does also the
power of decision; and a wise man differs from a fool quite as much by
conviction as by action. [159] Some of our perceptions are, however, of
such a kind that they at once oblige us to bestow on them assent,
compelling us not only to regard them as probable, but also as true
[160] and conformable to the actual nature of things. Such perceptions
produce in us that strength of conviction which the Stoics call a
conception; they are therefore termed conceptional perceptions.
Whenever a perception forces itself upon us in this irresistible form,
we are no longer dealing with a fiction of the imagination, but with
something real; but whenever the strength of conviction is wanting, we
cannot be sure of the truth of our perception. Or, expressing the same
idea in the language of Stoicism, conceptional or irresistible
perceptions, φαντασίαι καταληπτικαὶ, are the standard of truth. [161]
The test of irresistibility [(γ) Primary conceptions a standard as well
as irresistible perceptions.] (κατάληψις) was, in the first place,
understood to apply to sensations from without, such sensations,
according to the Stoic view, alone supplying the material for
knowledge. An equal degree of certainty was, however, attached to terms
deduced from originally true data, either by the universal and natural
exercise of thought, or by scientific processes of proof. Now, since
among these derivative terms some—the primary conceptions (κοιναὶ
ἔννοιαι), for instance—serve as the basis for deriving others, it may
in a certain sense be asserted that sensation and primary conceptions
are both standards of truth. [162] In strict accuracy, neither
sensation nor primary conceptions (πρόληψεις) can be called standards.
The real standard, whereby the truth of a perception is ascertained,
consists in the power, inherent in certain perceptions, of carrying
conviction—τὸ καταληπτικὸν—a power which belongs, in the first place,
to sensations, whether of objects without or within, and, in the next
place, to primary conceptions formed from them in a natural way—κοιναὶ
ἔννοιαι or προλήψεις. On the other hand, conceptions and terms formed
artificially can only have their truth established by being subjected
to a scientific process of proof. How, after these statements, the
Stoics could attribute a greater strength of conviction to artificial
than to primary conceptions; [163] how they could raise doubts as to
the trustworthiness of simple sensations, [164] is one of the paradoxes
of the Stoic system, which prove the existence, as in so many other
systems, of a double current of thought. There is, on the one hand, a
seeking for what is innate and original, a going back to nature, an
aversion to everything artificial and of human device, inherited by
Stoicism from its ancestral Cynicism. On the other hand, there is a
desire to supplement the Cynic appeal to nature by a higher culture,
and to assign scientific reasons for truths which the Cynics laid down
as self-evident.
The latter tendency will alone explain the care and precision which the
Stoics devoted to studying the forms and rules which govern
intellectual processes. Attention to this branch of study may be
noticed in Zeno and his immediate successors at the first separation of
Stoicism from Cynicism. [165] Aristo is the only Stoic who is opposed
to it, his whole habit of mind being purely that of a Cynic. In
Chrysippus it attained its greatest development, and by Chrysippus the
formal logic of the Stoics reached scientific completeness. In later
times, when Stoicism reverted more nearly to its original Cynic type,
and appealed directly to the immediate suggestions of the mind, it lost
its interest in logic, as may be observed in Musonius, Epictetus, and
others. For the present, however, let it suffice to consider the logic
of Chrysippus, as far as that is known to us.
[C. Formal logic.]
[(1) Utterance in general.]
The term formal logic is here used to express those investigations
which the Stoics included under the doctrine of utterance. [166] The
common object of those enquiries is that which is thought, or, as the
Stoics called it, that which is uttered (λεκτόν), understanding thereby
the substance of thought—thought regarded by itself as a distinct
something, differing alike from the external object to which it refers,
from the sound by which it is expressed, and from the power of mind
which produces it. For this reason, they maintain that only utterance
is not material; things are always material; even the process of
thought consists in a material change within the soul, and an uttered
word, in a certain movement of the atmosphere. [167] A question is here
suggested in passing, which should not be lost sight of, viz. How far
was it correct for the Stoics to speak of thoughts as existing, seeing
they are not material, since, according to their teaching, reality only
belongs to material things? [168]
Utterance may be either perfect or imperfect. It is perfect when it
contains a proposition; imperfect when the proposition is incomplete.
[169] The portion of logic, therefore, which treats of utterance falls
into two parts, devoted respectively to the consideration of complete
and incomplete expression.
[(2) Incomplete expression.]
[(a) The grammar of words.]
In the section devoted to incomplete expression, much is found which we
should include under grammar rather than under logic. Thus all
incomplete expressions are divided into two groups—one group includes
proper names and adjectives, the other includes verbs. [170] These two
groups are used respectively to express what is essential and what is
accidental, [171] and are again divided into a number of subdivisions
and varieties. [172] To this part of logic investigations into the
formation and division of conceptions, and the doctrine of the
categories, properly belong; but it cannot be said with certainty what
place they occupy in the logic of the Stoics. [173]
Certain it is that these researches introduced little new matter. All
that is known of the Stoic views in reference to the formation, the
mutual relation and the analysis of conceptions, differs only from the
corresponding parts in the teaching of Aristotle by the change of a few
expressions, and a slightly altered order of treatment. [174]
[(b) The Stoic Categories.]
Of greater importance is the Stoic doctrine of the categories. [175] In
this branch of logic, the Stoics again follow Aristotle, but not
without deviating from him in three points. Aristotle referred his
categories to no higher conception, but looked upon them severally as
the highest class-conceptions; the Stoics referred them all to one
higher conception. Aristotle enumerated ten categories; the Stoics
thought that they could do with four, [176] which four only partially
coincide with those of Aristotle. Aristotle placed the categories side
by side, as co-ordinate, so that no object could come under a second
category in the same respect in which it came under the first one;
[177] the Stoics placed them one under the other, as subordinate, so
that every preceding category is more accurately determined by the next
succeeding one.
[(α) Highest Conception—an indefinite Something.]
The highest conception of all was apparently by the older Stoics
declared to be the conception of Being. Since, however, speaking
strictly, only what is material can be said to have any being, and many
of our notions refer to incorporeal and therefore unreal objects, the
conception of Something [178] was in later times put in the place of
the conception of Being. This indefinite Something comprehends alike
what is material and what is not material—in other words, what has
being and what has not being; and the Stoics appear to have made this
contrast the basis of a real division of things. [179] When it becomes
a question, however, of formal elementary conceptions or categories,
other points are emphasised which have no connection with the division
into things material and things not material. Of this kind are the four
highest conceptions, [180]—all subordinate to the conception of
Something, viz. subject-matter or substance (τὸ ὑποκείμενον) property
or form (τὸ ποιὸν), variety (τὸ πὼς ἔχον), and variety of relation (τὸ
πρός τί πως ἔχον). [181]
[(β) Category of subject-matter or substance.]
The first of these categories [182] denotes the subject-matter of
things in themselves (τὸ ὑποκείμενον), the material of which they are
made, irrespective of any and every quality, [183] the something which
underlies all definite being, and which alone has a substantial value.
[184] Following Aristotle, the Stoics distinguish, [185] in this
category of matter, between matter in general, or universal matter, and
the particular matter or material out of which individual things are
made. The former alone is incapable of being increased or diminished.
Far otherwise is the material of which particular things are made. This
can be increased and diminished, and, indeed, is ever undergoing
change; so much so, that the only feature which continues the same
during the whole term of its existence [186] and constitutes its
identity, is its quality.
[(γ) The category of property.]
The second category, that of property [187] or form, comprises all
those essential attributes, by means of which a definite character is
impressed on matter otherwise indeterminate. [188] If the definite
character be one which belongs to a group or class, it is called a
common quality—κοινῶς ποιόν·—or, if it be something peculiar and
distinctive, it is called a distinctive quality—ἰδίως ποιόν. [189]
Properties therefore combined with matter constitute the special
materials out of which individual things are made; [190] and quality in
this combination (ποιόν), corresponds, as Trendelenburg has well shown,
[191] with the form (εἶδος) of Aristotle. [192] It may, in fact, like
that, be described as the active and efficient part of a thing. [193]
Aristotle’s form, however, expresses only the non-material side of a
thing, whereas quality is regarded by the Stoics as something
material—in fact, as an air-current. [194] Hence the mode in which a
quality is conceived to reside in matter is that of an intermingling of
elements. [195] The same theory of intermingling applies of course to
the union of several properties in one and the same matter, [196] and
likewise to the combination of several attributes to produce a single
conception of quality. [197] In all cases the relation is supposed to
be materialistic, and is explained by the doctrine of the mutual
interpenetration of material things. [198] This explanation, indeed,
could not apply to every kind of attributes. Unable to dispense
entirely with things not material, [199] the Stoics were obliged to
admit the existence of attributes belonging to immaterial things, these
attributes being, of course, themselves not material. [200] What idea
they formed to themselves of these incorporeal attributes, when reality
was considered to belong only to things corporeal, it is, of course,
impossible for us to say. [201]
[(δ) The categories of variety and variety of relation.]
The two remaining categories include everything which may be excluded
from the conception of a thing on the ground of being either
non-essential or accidental. In as far as such things belong to an
object taken by itself alone, they come under the category of variety
(πὼς ἔχον); but when they belong to it, because of its relation to
something else, they come under the category of variety of relation
(πρός τί πως ἔχον). Variety includes all accidental qualities, which
can be assigned to any object independently of its relation to any
other object. [202] Size, colour, place, time, action, passion,
possession, motion, state, in short, all the Aristotelian categories,
with the exception of substance, whenever they apply to an object
independently of its relation to other objects, belong to the category
of variety [203] (πὼς ἔχον). On the other hand, those features and
states which are purely relative—such as right and left, sonship and
fatherhood, &c.—come under the category of variety of relation (πρός τί
πως ἔχον); and from this category the simple notion of relation (πρὸς
τὶ) must be distinguished. Simple relation (πρὸς τὶ) is not treated as
a distinct category, since it includes not only accidental relations,
but also those essential properties (ποιὰ) which presuppose a definite
relation to something else—such as knowledge and perception. [204]
[(c) Relation of the categories to one another.]
The relation of these four categories to one another is such, that each
preceding category is included in the one next following, and receives
from it a more definite character. [205] Substance never occurs in
reality without property, but has always some definite quality to give
it a character. On the other hand, property is never met with alone,
but always in connection with some subject-matter. [206] Variety
presupposes some definite substance, and variety of relation supposes
the existence of variety. [207] It will hereafter be seen how closely
these deductions, and, indeed, the whole doctrine of the categories,
depend on the metaphysical peculiarities of the Stoic system.
[(3) Complete utterance.]
[(a) Judgment.]
Passing from incomplete to complete utterance, we come, in the first
place, to sentences or propositions, [208] all the various kinds of
which, as they may be deduced from the different forms of syntax, are
enumerated by the Stoics with the greatest precision. [209] Detailed
information is, however, only forthcoming in reference to the theory of
judgment (ἀξίωμα), which certainly occupied the chief and most
important place in their speculations. A judgment is a perfect
utterance, which is either true or false. [210] Judgments are divided
into two classes: simple judgments, and composite judgments. [211] By a
simple judgment the Stoics understand a judgment which is purely
categorical. [212] Under the head of composite judgments are comprised
hypothetical, corroborative, copulative, disjunctive, comparative, and
causal [(α) Simple judgment.] judgments. [213] In the case of simple
judgments, a greater or less definiteness of expression is substituted
in place of the ordinary difference in respect of quantity; [214] and
with regard to quality, they not only make a distinction between
affirmative and negative judgments, [215] but, following the various
forms of language, they speak of judgments of general negation,
judgments of particular negation, and judgments of double negation.
[216] Only affirmative and negative judgments have a contradictory
relation to one another; all other judgments stand to each other in the
relation of contraries. [217] Of two propositions which are related as
contradictories, according to the old rule, one must be true and the
other false. [218]
[(β) Composite judgments.]
Among composite judgments the most important are the hypothetical and
the disjunctive. As regards the latter, next to no information has
reached us. [219] A hypothetical judgment (συνημμένον) is a judgment
consisting of two clauses, connected by the conjunction ‘if,’ and
related to one another as cause and effect; the former being called the
leading (ἡγούμενον), and the latter the concluding or inferential
clause (λῆγον). [220] In the correctness of the inference the truth of
a hypothetical judgment consists. As to the conditions upon which the
accuracy of an inference rests, different opinions were entertained
within the Stoic School itself. [221] In as far as the leading clause
states something, from the existence of which an inference may be drawn
for the statement in the concluding clause, it is also called an
indication or suggestive sign. [222]
[(γ) Modality of judgments.]
The modality of judgments, which engaged the attention of Aristotle and
his immediate pupils so much, was likewise treated by the Stoics at
considerable length; but of this branch of enquiry so much only is
known to us as concerns possible and necessary judgments, and it is the
outcome chiefly of the contest between Chrysippus and the Megarian
Diodorus. [223] It is in itself of no great value. By the Stoics,
nevertheless, great value was attached to it, in the hope of escaping
thereby the difficulties which necessarily result from their views on
freedom and necessity. [224]
[(b) Inference.]
In their theory of illation, [225] to which the Stoics attached special
value, and on which they greatly prided themselves, [226] chief
attention was paid to hypothetical and disjunctive inferences. [227] In
regard to these forms of inference, the rules they laid down are well
known: [228] and from these forms they invariably take their examples,
even when treating of inference [(α) Hypothetical inference the
original form.] in general. [229] According to Alexander, [230] the
hypothetical and disjunctive forms are held to be the only regular
forms of inference; [231] the categorical form is considered correct in
point of fact, but defective in syllogistic form. [232] In hypothetical
inferences a distinction was also made between such as are connected
and such as are disconnected. [233] In connected inferences the Stoics
look principally at the greater or less accuracy of expression, [234]
and partly at the difference between correctness of form and truth of
matter. [235] They also remark that true conclusions do not always
extend the field of knowledge; and that those which do frequently
depend on reasons conclusive for the individual, but not on proofs
universally acknowledged. [236] The main point, however, to be
considered in dividing inferences is their [(β) The five simple forms
of hypothetical inference.] logical form. There are, according to
Chrysippus, [237] who herein adopted the division of Theophrastus, five
original forms of hypothetical inference, the accuracy of which is
beyond dispute, and to which all other forms of inference may be
referred and by which they may be tested. [238] Yet even among these
five, importance is attached to some in which the same sentence is
repeated tautologically in the form of a conclusion, [239] which proves
how mechanical and barren must have been the formalism with which the
Stoic logic abounds.
[(γ) Composite forms of inference.]
The combination of these five simple forms of inference gives rise to
the composite forms of inference, [240] all of which may be again
resolved into their simple forms. [241] Among composite forms of
inference, those composed of similar parts are distinguished from those
composed of dissimilar parts; [242] in the treatment of the former,
however, such a useless formality is displayed, that it is hard to say
what meaning the Stoics attached to them. [243] If two or more
inferences, the conclusion of one of which is the first premiss of the
other, are so combined that the judgment which constitutes the
conclusion and premiss at once is omitted in each case, the result is a
Sorites or Chain-inference. The rules prescribed by the Peripatetics
for the Chain-inference are developed by the Stoics with a minuteness
far transcending all the requirements of science. [244] With these [(δ)
Inference from a single premiss.] composite forms of inference
Antipater contrasted other forms having only a single premiss, [245]
but it was an addition to the field of logic of very doubtful worth. On
a few other points connected with the Stoic theory of illation, we have
very imperfect information. [246] The loss, however, is not to be
regretted, seeing that in what we already possess there is conclusive
evidence that the objections brought against the Stoic logic were
really well deserved, because of the microscopic care expended by them
on the most worthless logical forms. [247]
[(c) Refutation of fallacies.]
Next to describing inferences which are valid, another subject engaged
the close attention of the Stoics, and afforded opportunity for
displaying their dialectical subtlety. This is the enumeration and
refutation of false inferences, [248] and in particular the exposing of
the many fallacies which had become current since the age of the
Sophists and Megarians. In this department, as might be expected,
Chrysippus led the way. [249] Not that Chrysippus was always able to
overcome the difficulties that arose; witness his remarkable attitude
towards the Chain-inference, from which he thought to escape by
withholding judgment. [250] The fallacies, however, to which the Stoics
devoted their attention, and the way in which they met them, need not
occupy our attention further. [251]
[D. Estimate of Stoic Logic.]
[(1) Its shortcomings.]
In all these researches the Stoics were striving to find firm ground
for a scientific process of proof. Great as was the value which they
attached to such a process, they nevertheless admitted, as Aristotle
had done before, that everything could not be proved. Here was their
weak point. Instead, however, of strengthening this weak point by means
of induction, and endeavouring to obtain a more complete theory of
induction, they were content with conjectural data, sometimes
self-evident, at other times depending for their truth on the truth of
their inferences. [252] Thus, their theory of method, like their theory
of knowledge, ended by an ultimate appeal to what is directly certain.
[(2) Its value.]
No very high estimate can therefore be formed of the formal logic of
the Stoics. Incomplete as our knowledge of that logic may be, still
what is known is enough to determine the judgment absolutely. We see
indeed that the greatest care was expended by the Stoics since the time
of Chrysippus in tracing the forms of intellectual procedure into their
minutest ramifications, and referring them to fixed types. At the same
time, we see that the real business of logic was lost sight of in the
process, the business of portraying the operations of thought, and
giving its laws, whilst the most useless trifling with forms was
recklessly indulged in. The Stoics can have made no discoveries of
importance even as to logical forms, or they would not have been passed
over by writers ever on the alert to note the slightest deviation from
the Aristotelian logic. Hence the whole contribution of the Stoics to
the field of logic consists in their having clothed the logic of the
Peripatetics with a new terminology, and having developed certain parts
of it with painful minuteness, whilst they wholly neglected other
parts, as was the fate of the part treating of inference. Assuredly it
was no improvement for Chrysippus to regard the hypothetical rather
than the categorical as the original form of inference. Making every
allowance for the extension of the field of logic, in scientific
precision it lost more than it gained by the labours of Chrysippus. The
history of philosophy cannot pass over in silence this branch of the
Stoic system, so carefully cultivated by the Stoics themselves, and so
characteristic of their intellectual attitude. Yet, when all has been
said, the Stoic logic is only an outpost of their system, and the care
which was lavished on it since the time of Chrysippus indicates the
decline of intellectual originality.