Logic

Logic is the science and art which so directs the mind in the
process of reasoning and subsidiary processes as to enable it to
attain clearness, consistency, and validity in those processes.
The aim of logic is to secure clearness in the definition and
arrangement of our ideas and other mental images, consistency in
our judgments, and validity in our processes of inference.

I. THE NAME

The Greek word logos, meaning "reason", is the origin of the term
logic--logike (techen, pragmateia, or episteme, understood), as
the name of a science or art, first occurs in the writings of the
Stoics (see STOIC PHILOSOPHY). Aristotle, the founder of the
science, designates it as "analytic", and the Epicureans (see
EPICUREANISM) use the term canonic. From the time of Cicero,
however, the word logic is used almost without exception to
designate this science. The names dialectic and analytic are also
used.

II. THE DEFINITION

It is a curious fact that, although logic is the science which
treats of definition, logicians are not agreed as to how logic
itself should be defined. There are, in all, about two hundred
different definitions of logic. It would, of course, be impossible
to enumerate even the principal definitions here. It will be
sufficient to mention and discuss a few typical ones.

A. Port Royal logic

The Port Royal logic ("L'Art de penser", published 1662) defines
logic as "the art of using reason well in the acquisition of the
knowledge of things, both for one's own instruction and that of
others." More briefly "Logic is the art of reasoning." The latter
is Arnauld's definition. Definitions of this type are considered
too narrow, both because they define logic in terms of art, not
leaving room for its claim to be considered a science, and
because, by the use of the term reasoning, they restrict the scope
of logic to one class of mental processes.

Hegel

Hegel (see HEGELIANISM) goes to the other extreme when he defines
logic as "the science of the pure idea." By idea he understands
all reality, so that for him logic includes the science of
subjective reality (logic of mental concepts) and the science of
objective reality (logic of being, metaphysics). In like manner
the definitions which fail to distinguish between logic and
psychology, defining logic as "the science of mental processes",
or "the science of the operations of the mind", are too wide.
Definitions which characterize logic as "the science of sciences",
"the art of arts", are also too wide: they set up too large a
claim for logic.

C. St. Thomas Aquinas

In his commentary on Aristotle's logical treatises (" In Post.
Anal.", lect. i, Leonine ed., I, 138), he says: "Ars qutedam
necessaria est, quae sit directiva ipsius actus rationis, per quam
scilicet homo in ipso actu rationis ordinate faciliter et sine
errore procedat. Et haec ars est logica, id est rationalis
scientia." Combining those two sentences, we may render St.
Thomas's definition as follows: "Logic is the science and art
which directs the act of the reason, by which a man in the
exercise of his reason is enabled to proceed without error,
confusion, or unnecessary difficulty." Taking reason in its
broadest sense, so as to include all the operations of the mind
which are strictly cognitive, namely, the formation of mental
images, judgment, and ratiocination, we may expand St. Thomas'
definition and define logic as "the science and art which so
directs the mind in the process of reasoning and subsidiary
processes as to enable it to attain clearness (or order),
consistency, and validity in those processes". Logic is
essentially directive. Therein it differs from psychology, which
is essentially speculative or theoretical, and which concerns
itself only in an Incidental and secondary manner with the
direction of mental processes. Logic deals with processes of the
mind. Therein it differs from metaphysics, which has for its field
of inquiry and speculation the whole universe of being (see
METAPHYSICS). Logic deals with mental processes in relation to
truth or, more particularly, in relation to the attainment and
exposition of truth by processes which aim at being valid, clear,
orderly, and consistent. Therein it differs from ethics, which
treats of human actions, external deeds as well as thoughts, in
relation to man's final destiny. Validity, clearness, consistency,
and order are logical qualities of thought, goodness and evil are
ethical qualities. Finally, logic is not to be confounded with
rhetoric. Rhetoric, in the old meaning of the word, was the art of
persuasion; it used all the devices, such as emotional appeal,
verbal arrangement, etc., in order to bring about a state of mind
which had reference to action primarily, and to conviction only in
a secondary sense. Logic is the science and art of conviction it
uses only arguments, discarding emotional appeal and employing
merely words as the symbols of thoughts.

The question whether logic is a science or an art is now generally
decided by asserting that it is both. It is a science, in so far
as it not merely formulates rules for right thinking, but deduces
those rules from general principles which are based on the nature
of mind and of truth. It is an art, in so far as it is directly
and immediately related to performance, namely, to the acts of the
mind. As the fine arts direct the painter or the sculptor in the
actions by which he aims at producing a beautiful picture or a
beautiful statue, so logic directs the thinker in the actions by
which he aims at attaining truth, or expounding truth which he has
attained.

III. DIVISION OF LOGIC

The traditional mode of dividing logic, into "formal" and
"material", is maintained in many modern treatises on the subject.
In formal logic the processes of thought are studied independently
of, or without consideration of, their content. In material logic
the chief question is the truth of the content of mental
processes. An example from arithmetic will serve to illustrate the
function of formal logic. When we add two and two, and pronounce
the result to be four, we are dealing with a process of addition
in its formal aspect, without paying attention to the content. The
process is valid whatever the content may be, whether the "two and
two "refer to books, horses, trees, or circles. This is precisely
how we study judgments and arguments in logic. From the judgment
"All A is B" we infer "Therefore some B is A"; and the process is
valid whether the original proposition be "All circles are round"
or "All lions are carnivorous". In material logic, on the
contrary, we inquire into the content of the judgments or premises
and endeavour to determine whether they are true or false.
Material logic was styled by the old writers "major logic",
"critical logic", or simply" criticism". In recent times the word
epistemology (science of knowledge), meaning an inquiry into the
value of knowledge, has come into general use, and designates that
portion of philosophy which inquires into the objective value of
our concepts, the import and value of judgments and reasoning, the
criteria of truth, the nature of evidence, certitude, etc.
Whenever this new term is adopted there is a tendency to restrict
the term logic to mean merely formal logic. Formal logic studies
concepts,and other mental images, for the purpose of securing
clearness and order among those contents of the mind. It studies
judgments for the purpose of showing when and how they are
consistent or inconsistent, that is, when one may be inferred from
another (conversion), and when they are opposed (opposition) . It
studies the two kinds of reasoning, deductive and inductive, so as
to direct the mind to use these processes validly. Finally, it
studies sophisms (or fallacies) and method for the purpose of
showing what errors are to be avoided, and what arrangement is to
be followed in a complex series of reasoning processes. But, while
it is true in general that in all these tasks formal logic
preserves its purely formal character, and does not inquire into
the content of thought, nevertheless, in dealing with inductive
reasoning and in laying down the rules for definition and
division, formal logic does take account of the matter of thought.
For this reason, it seems desirable to abandon the old distinction
between formal and material, to designate as logic what was
formerly called formal logic, and to reserve the term epistemology
for that portion of philosophy which, while inquiring into the
value of human knowledge in general, covers the ground which was
the domain of material logic.

There remain certain kinds of logic which are not included under
the heads formal and material. Transcendental logic (Kant) is the
inquiry into human knowledge for the purpose of determining what
elements or factors in human thought are a priori, that is,
independent of experience. Symbolic logic (Lambert, Boole) is an
application of mathematical methods to the processes of thought.
It uses certain conventional symbols to represent terms,
propositions, and the relations among them, and then, without any
further reference to the laws of thought, applies the rules and
methods of the mathematical calculus (Venn, "Symbolic Logic",
London, 1881). Applied logic, in the narrower sense, is synonymous
with material logic in the wider sense, it means logic applied to
the study of the natural sciences, Iogic applied to education,
logic applied to the study of law, etc. Natural logic is that
native power of the mind by which most persons are competent to
judge correctly and reason validly about the affairs and interests
of everyday life; it is contrasted with scientific logic, which is
logic as a science and cultivated art.

IV. HISTORY OF LOGIC

The history of logic possesses a more than ordinary interest,
because, on the one hand, every change in the point of view of the
metaphysician and the psychologist tended to produce a
corresponding change in logical theory and practice, while, on the
other hand, changes in logical method and procedure tended to
affect the conclusions as well as the method of the philosopher.
Notwithstanding these tendencies towards variation, the science of
logic has undergone very few radical changes from the beginning of
its history.

A. The Nyaya

A system of philosophy which was studied in India in the fifth
century B.C., though it is perhaps, of much older date, takes its
name from the word nyaya, meaning logical argument, or syllogism.
This philosophy, like all the Indian systems, busied itself with
the Problem of the deliverance of the soul from bondage, and its
solution was that the soul is to be freed from the trammels of
matter by means of systematic reasoning. This view of the question
led naturally to an analysis of the methods of thinking, and to
the construction of a type of reasoning which bears a remote
resemblance to the syllogism. The nyaya, or Indian syllogism, as
it is sometimes called, consists of five propositions. If, for
instance, one wishes to prove that the hill is on fire, one begins
with the assertion: "The hill is on fire." Next, the reason is
given: "For it smokes." Then comes an instance, "Like the kitchen
fire"; which is followed by the application, "So also the hill
smokes." Finally comes the conclusion, "Therefore it is on fire."
Between this and the clear-cut Aristotelean syllogism, with its
major and minor premises and conclusion, there is all the
difference that exists between the Oriental and the Greek mode of
thinking. It is hardly necessary to say that there is no
historical evidence that Aristotle was in any way influenced in
his logic by Gotama, the reputed author of the nyaya.

B. Pre-Aristotelean Logic in Greece

The first philosophers of Greece devoted attention exclusively to
the problem of the origin of the universe (see IONIAN SCHOOL OF
PHILOSOPHY). The Eleatics, especially Zeno of Elea, the Sophists,
and the Megarians developed the art of argumentation to a high
degree of perfection. Zeno was especially remarkable in this
respect, and is sometimes styled the Founder of Dialectic. None of
these, however, formulated laws or rules of reasoning. The same is
true of Socrates and Plato, although the former laid great stress
on definition and induction, and the latter exalted dialectic, or
discussion, into an important instrument of philosophical
knowledge.

C. Aristotle, the Founder of Logic

In the six treatises which he devoted to the subject, Aristotle
examined and analysed the thinking processes for the purpose of
formulating the laws of thought. These treatises are

�  "The Categories",

�  "Interpretation",

�  "Prior Analytics",

�  "Posterior Analytics",

�  "Topics", and

�  "Sophisms". These were afterwards given the title of "Organon",
or "Instrument of Knowledge"; this designation, however, did not
come into common use until the fifteenth century.

The first four treatises contain, with occasional excursions into
the domain of grammar and metaphysics, the science of formal logic
essentially the same as it is taught at the present day. The
"Topics" and the "Sophisms" contain the applications of logic to
argumentation and the refutation of fallacies. In conformity with
the fundamental principle of his theory of knowledge, namely, that
all our knowledge comes from experience, Aristotle recognizes the
importance of inductive reasoning, that is to say, reasoning from
particular instances to general principles. If he and his
followers did not develop more fully this portion of logic, it was
not because they did not recognize its importance in principle.
His claim to the title of Founder of Logic has never been
seriously disputed the most that his opponents in the modern era
could do was to set up rival systems in which induction was to
supplant syllogistic reasoning. One of the devices of the
opponents of scholasticism is to identify the Schoolmen and
Aristotle with the advocacy of an exclusively deductive logic.

D. Post-Aristotelean Logicians Among the Greeks

Among the immediate disciples of Aristotle, Theophrastus and
Eudemus devoted special attention to logic. To the former is
sometimes attributed the invention of the hypothetical syllogism,
although the same claim is sometimes made for the Stoics. The
latter, to whom, probably, we owe the name logic, recognized this
science as one of the constitutive parts of philosophy. They
included in it dialectic and rhetoric, or the science of
argumentation and the science of persuasion. They busied
themselves also with the question of the criterion of truth, which
is still an important problem in major logic, or, as it is now
called, epistemology. Undoubtedly, they improved on Aristotle's
logic in many points of detail; but to what extent, and in what
respect, is a matter of conjecture, owing to the loss of the
voluminous Stoic treatises on logic. Their rivals, the Epicureans
(see EPICUREANISM) professed a contempt for logic-or "canonic", as
they styled it. They maintained that it is an adjunct of physics,
and that a knowledge of physical phenomena acquired through the
senses is the only knowledge that is of value in the pursuit of
happiness. After the Stoics and the Epicureans came the
commentators. These may, for convenience, be divided into the
Greeks and the Latins. The Greeks from Alexander of Aphrodisias,
in the second, to St. John of Damascus in the eighth century of
our era, flourished at Athens, at Alexandria, and in Asia Minor.
With Photius, in the ninth century, the scene is shifted to
Constantinople. To the first period belong Alexander of
Aphrodisias, known as "the Commentator" Themistius, David the
Armenian, Philoponus, Simplicius and Porphyry, author of the
Isagoge (Eisagoge), or "Introduction" to the logic of Aristotle.
In this work the author, by his explicit enumeration of the five
predicables and his comment thereon, flung a challenge to the
medieval logicians, which they took up in the famous controversy
concerning universals (see UNIVERSALS). To the second period
belong Photius, Michael Psellus the younger (eleventh century),
Nicephorus Blemmydes, George Pachymeres, and Leo Magentinus
(thirteenth century). All these did little more than abridge,
explain, and defend the text of the Aristotelean works on logic.
An exception should, perhaps, be made in favour of the physician
Galen (second century), who is said to have introduced the fourth
syllogistic figure, and who wrote a special work, "On Fallacies of
Diction".

E. Latin Commentators

Among the Latin commentators on Aristotle we find almost in every
case more originality and more inclination to add to the science
of logic than we do in the case of the Greeks. After the taking of
Athens by Sulla (84 B.C.) the works of Aristotle were carried to
Rome, where they were arranged and edited by Andronicus of Rhodes
(see ARISTOTLE). The first logical treatise in Latin is Cicero's
abridgment of the "Topics". Then came a long period of inactivity.
About A.D.160, Apuleius wrote a short account of the
"Interpretation". In the middle of the fourth century Marius
Victorinus translated Porphyry's "Isagoge". To the time of St.
Augustine belong the treatises "Categoriae Decem" and "Principia
Dialectica". Both were attributed to St. Augustine, though the
first is certainly spurious, and the second of doubtful
authenticity. They were very often
Transcribed in the early Middle Ages, and the logical treatises of
the ninth and tenth centuries make very free use of their
contents. The most popular however, of all the Latin works on
logic was the curious medley of prose and verse "De Nuptiis
Mercurii et Philologiae" by Marcianus Capella (about A. D. 475).
In it dialectic is treated as one of the seven liberal arts (see
ARTS, THE SEVEN LIBERAL), and that portion of the work was the
text in all the early medieval schools of logic. Another writer on
logic who exerted a widespread influence during the first period
of Scholasticism was Boethius (470 524), who wrote two
commentaries on the "Isagoge" of Porphyry, two on Aristotle's
"Interpretation", and one on the "Categories". Besides, he wrote
the original treatises,"On Categorical Syllogisms", "On Division",
and "On Topical Differences", and translated several portions of
Aristotle's logical works. In fact, it was principally through his
translations that the early Scholastic writers, who as a rule,
were entirely ignorant of Greek, had access to Aristotle's
writings. Cassiodorus a contemporary of Boethius, wrote a
treatise, "On the Seven Liberal Arts", in which, in the portion
devoted to dialectic, he gave a summary and analysis of the
Aristotelean and Porphyrian writings on logic. Isidore of Seville
(died 636), Venerable Bede (673-735) and Alcuin (736-804), the
forerunners of the Scholastics, were content with abridging in
their logical works the writings of Boethius and Cassiodorus.

F. The Scholastics

The first masters of the schools in the age of Charlemagne and the
century immediately following were not acquainted at first hand
with Aristotle's works. They used the works and translations of
Boethius, the pseudo-Augustinian treatises mentioned above, and
the work by Marcianus Capella. Little by little their interest
became centred on the metaphysical and psychological problems
suggested in those treatises especially on the problem of
universals and the conflict between Realism and Nominalism. As a
consequence of this shifting of the centre of interest, very
little was done towards perfecting the technic of logic, and there
is a very noticeable dearth of original work during the ninth and
tenth centuries. John Scotus Eriugena, Eric and Remi of Auxerre,
and the teachers at St. Gall in Switzerland confined their
activity to glossing and commenting on the traditional texts,
especially Pseudo-Augustine and Marcianus Capella. In the case of
the St. Gall teachers we have however, by way of exception, a work
on logic, which bears evident traces of the influence of Eriugena,
and a collection of mnemonic verses containing the nineteen valid
syllogisms.

Roscelin (about 1050-1100), by his outspoken profession of
Nominalism concentrated the attention of his contemporaries and
immediate successors on the problem of universals. In the
discussion of that problem the art of dialectical disputation was
developed, and a taste for argumentation was fostered, but none of
the dialecticians of the twelfth century, with the exception of
Abelard, contributed to the advancement of the science of logic.
This Abelard did in several ways. In his work to which Cousin gave
the title "Dialectica", and in his commentaries, he strove to
widen the scope and enhance the utility of logic as a science. Not
only is it the science of disputation, but also the science of
discovery, by means of which the arguments supplied by a study of
nature are examined. The principal application of logic, however,
is in the discussion of religious truth. Here Abelard, citing the
authority of St. Augustine, contends that the methods of dialectic
are applicable to the discussion of all truth, revealed as well as
rational; they are applicable even to the mysteries of faith. In
principle he was right, although in practice he went further than
the example of St. Augustine would warrant him in going. His
subsequent condemnation had for its ground, not the use of
dialectic in theology, but the excessive use of dialectic to the
point of rationalism. Abelard, it should be noted, was acquainted
only with those treatises of Aristotle which had been translated
by Boethius, and which constituted the logica vetus. His
contemporary, Gilbert de la Porree (q.v.), added to the old logic
a work entitled "Liber Sex Principiorum", a treatise on the last
six of the Aristotelean Categories. Towards the middle of the
twelfth century the remainder of the Aristotelean "Organon" became
known, so that the logic of the schools, thenceforth known as
logica nova, now contained:

�  Aristotle's "Categories" and "Interpretation" and Porphyry's
"Isagoge" (contents of the logica vetus);

�  Aristotle's "Analytics", "Topics", and "Sophisms";

�  Gilbert's "Liber Sex Principiorum".

This was the text in the schools when St. Thomas began to teach,
and it continued to be used until superseded by the logica
moderna, which embodied the contributions of Petrus Hispanus. The
first writer of importance who reveals an acquaintance with the
Aristotelean "Organon" in its entirety is John of Salisbury (died
1182), a disciple of Abelard, who explains and defends the
legitimate use of dialectic in his work "Metalogicus".

The definite triumph of Aristotelean logic in the schools of the
thirteenth century was influenced by the introduction into
Christian Europe of the complete works of Aristotle in Greek. The
occasion of this was the taking of Constantinople by the crusaders
in 1204. The Crusades had also the effect of bringing Christian
Europe into closer contact with the Arabian scholars who, ever
since the ninth century, had cultivated Aristotelean logic as well
as the neo-Platonic interpretation of Aristotle's metaphysics. It
was the Arabians who distinguished logica docens and logica utens.
The former is logic as a theoretical science; the latter is logic
as an applied art, practical logic. To them also is attributed the
distinction between first intentions and second intentions. The
Arabians, however, did not exert a determining influence on the
development of Scholastic logic; they contributed to that
development only in an external manner, by helping to make
Aristotelean literature accessible to Christian thinkers. St.
Thomas Aquinas and his teacher, Blessed Albertus Magnus (Albert
the Great) did signal service to Scholastic logic, not so much by
adding to its technical rules as by defining its scope and
determining the limits of its legitimate applications to theology.
They both composed commentaries on Aristotle's logical works and,
besides, wrote independent logical treatises. The work, however,
which bears the name "Summa Totius Logicae", and is found among
the "Opuscula" of St. Thomas, is now judged to be from the pen of
a disciple of his, Herve of Nedellac (Hervaeus Natalis). John Duns
Scotus was also a commentator on Aristotle's logic. His most
important original treatises on logic are "De Universalibus", in
which he goes over the ground covered by Porphyry in the
"Isagoge", and "Grammatica Speculativa". The latter is an
interesting contribution to critical logic.

The technic of logic received special attention from Petrus
Hispanus (Pope John XXI, died 1277), author of the "Summulae
Logicales". This is the first medieval work to cover the whole
ground of Aristotelean logic in an original way. All its
predecessors were merely summaries or abridgments of Aristotle's
works. In it occur the mnemonic lines, "Barbara, Celarent", etc.,
and nearly all the devices of a similar kind which are now used in
the study of logic. They are the first of the kind in the history
of logic, the lines in the ninth-century manuscript mentioned
above being verses to aid the memory, without the use of arbitrary
signs, such as the designation of types of propositlons by means
of vowels. And the credit of having introduced them is now almost
unanimously given to Petrus himself. The theory that he borrowed
them from a Greek work by Psellus (see above) is discredited by an
examination of the manuscripts, which shows that the Greek verses
are of later date than those in the "Summulae". In fact, it was
the Byzantine writer who copied the Parisian teacher, and not, as
Prantl contended, the Latin who borrowed from the Greek. William
of Occam (1280-1349) improved on the arrangement and method of the
"Summulae" in his "Summa Totius Logicae". He also made important
contributions to the doctrine of supposition of terms. He did not,
however, agree with St. Thomas and St. Albert the Great in their
definition of the scope and application of logic. His own
conception of the purpose of logic was sufficiently serious and
dignified. It was his followers, the Occamists of the fourteenth
and fifteenth centuries, who, by their abuse of dialectical
methods brought Scholastic logic into disrepute. One of the most
original of all the Scholastic logicians was Raymond Lully (1234-
1315). In his "Dialectica" he expounds clearly and concisely the
logic of Aristotle, together with the additions made to that
science by Petrus Hispanus. In his "Ars Magna", however, he
discards all the rules and prescriptions of the formal science,
and undertakes by means of his "logical machine" to demonstrate in
a perfectly mechanical way all truth, supernatural as well as
natural.

Scholastic logic, as may be seen from this sketch, did not modify
the logic of Aristotle in any essential manner. Nevertheless, the
logic of the Schools is an improvement on Aristotelean logic. The
Schoolmen made clear many points which were obscure in Aristotle's
works: for example, they determined more accurately than he did
the nature of logic and its place in the plan of sciences. This
was brought about naturally by the exigencies of theological
controversy. Moreover, the Schoolmen did much to fix the technical
meanings of terms in the modern languages, and, though the
scientific spirit of the ages that followed spurned the methods of
the Scholastic logicians, its own work was very much facilitated
by the efforts of the Scholastics to distinguish the
significations of words, and trace the relationship of language to
thought. Finally, to the Schoolmen logic owes the various memory-
aiding contrivances by the aid of which the task of teaching or
learning the technicalities of the science is greatly facilitated.

G. Modern Logic

The fifteenth century witnessed the first serious attempts to
revolt against the Aristotelean logic of the Schools. Humanists
like Ludovicus Vico and Laurentius Valla made the methods of the
Scholastic logicians the object of their merciless attack on
medievalism. Of more importance in the history of logic is the
attempt of Ramus (Pierre de La Ramee, 1515-72) to supplant the
traditional logic by a new method which he expounded in his works
"Aristotelicae Animadversiones" and "Scholae Dialecticae". Ramus
was imitated in Ireland by George Downame (or Downham), Bishop of
Derry, in the seventeenth century, and in the same century he had
a most distinguished follower in England in the person of John
Milton, who, in 1672, published "Artis Logicae Plenior Institutio
ad Petri Rami Methodum Concinnata". Ramus's innovations, however,
were far from receiving universal approval, even among
Protestants. Melanchthon's "Erotemata Dialectica", which was
substantially Aristotelean, was extensively used in the Protestant
schools, and exerted a wider influence than Ramus's
"Animadversiones". Francis Bacon (1561-1626) inaugurated a still
more formidable onslaught. Profiting by the hints thrown out by
his countryman and namesake, Roger Bacon (1214-1294), he attacked
the Aristotelean method, contending that it was utterly barren of
results in science, that it was, in fact, essentially
unscientific, and needed not so much to be reformed as to be
entirely supplanted by a new method. This he attempted to do in
his "Novum Organum", which was to introduce a new logic, an
inductive logic, to take the place of the deductive logic of
Aristotle and the Schoolmen. It is now recognized even by the
partisans of Bacon that he erred in two respects. He erred in
describing Aristotle's logic as exclusively deductive, and he
erred in claiming for the inductive method the ability to direct
the mind in scientific discovery and practical invention. Bacon
did not succeed in overthrowing the authority of Aristotle.
Neither did Descartes (1596-1649), who was as desirous to make
logic serve the purposes of the mathematician as Bacon was to make
it serve the cause of scientific discovery. The Port Royal Logic
("L'Art de penser" 1662), written by Descartes's disciples, is
essentially Aristotelean. So, though in a less degree are the
logical treatises of Hobbes (1588-1679) and Gassendi (1592-1655),
both of whom underwent the influence of Bacon's ideas. In the
seventeenth and eighteenth centuries, Father Buffier, Le Clerc
(Clericus), Wolff, and Lambert strove to modify the Aristotelean
logic in the direction of empiricism, sensism, or Leibnizian
innatism. In the treatises which they wrote on logic there is
nothing that one might consider of primary importance.

Kant and the other German Transcendentalists of the nineteenth
century took a more equitable view of Aristotle's services to the
science of logic. As a rule, they recognized the value of what he
had accomplished and, instead of trying to undo his work, they
attempted to supplement it. It is a question, however, whether
they did not do as much harm to logic in one way as Bacon and
Descartes did in another. By withdrawing from the domain of logic
what is empirical, and confining the science to an examination of
"the necessary laws of thought", the Transcendentalists gave
occasion to Mill and other Associationists to accuse logic of
being unreal, and out of touch with the needs of an age which was,
above all things, an age of empirical science. Most of the recent
German literature on logic is characterized by the amount of
attention which it pays either to historical inquiries, or to
inquiries into the value of knowledge, or to investigation of the
philosophical foundations of the laws of logic. It has added very
little to the technical portion of the science. In England, the
most important event in the history of logic in the nineteenth
century was the publication, in 1843, of John Stuart Mill's
"System of Logic". Mill renewed all the claims put forward by
Bacon, and with some measure of success. At least, he brought
about a change in the method of teaching logic at the great
English seats of learning. Carrying Locke's empiricism to its
ultimate conclusion, and adopting the association theory of the
human mind, he rejected all necessary truth, discarded the
syllogism as not only useless but fallacious, and maintained that
all reasoning is from particulars to particulars. He did not make
many converts to these views, but he succeeded in giving inductive
logic a place in every textbook on logic published since his time.
Not so successful was the attempt of Sir William Hamilton to
establish a new logic (the "new analytic"), on the principle that
the predicate as well as the subject of a proposition should be
quantified. Nor, indeed, was he quite original in this: the idea
had been put forward in the seventeenth century by the Catholic
philosopher Caramuel (1606-82). Recent logical literature in
English has striven above all things to attain clearness,
intelligibility, and practical utility in its exposition of the
laws of thought. Whenever it indulges in speculation as to the
nature of mental processes, it is, of course, coloured by the
various philosophies of the time.

Indeed, the history of logic is interesting and profitable chiefly
because it shows how the philosophical theories influence the
method and the doctrine of the logician. The empiricism and
sensism of the English school, descending from Hobbes through
Locke, Hume, and the Associationists, could lead in logic to no
other conclusion than that to which it does lead in Mill's
rejection of the syllogism and of all necessary truth. On the
other hand, Descartes's exaltation of deduction and Leibniz's
adoption of the mathematical method have their origin in that
doctrine of innatism which is the opposite of empiricism. Again,
the domination of industrialism, and the insistence for
recognition on the part of the social economist, have had in our
own day the effect of pushing logic more and more towards the
position of a purveyor of rules for scientific discovery and
practical invention. The materialism of the last half of the
nineteenth century demanded that logic prove its utility in a
practical way. Hence the prominence given to induction. But, of
all the crises through which logic has passed, the most
interesting is that which is known as the "Storm and Stress of
Scholasticism", in which mysticism on the one side rejected
dialectic as "the devil's art", and maintained that "God did not
choose logic as a means of saving his people", while rationalism
on the other side set no bounds to the use of logic, going so far
as to place it on a plane with Divine faith. Out of this conflict
issued the Scholasticism of the thirteenth century, which gave due
credit to the mystic contention in so far as that contention was
sound, and at the same time acknowledged freely the claims of
rationalism within the limits of orthodoxy and of reason. St.
Thomas and his contemporaries looked upon logic as an instrument
for the discovery and exposition of natural truth. They
considered, moreover, that it is the instrument by which the
theologian is enabled to expound, systematize, and defend revealed
truth. This view of the theological use of logic is the basis for
the charge of intellectualism which Modernist philosophers imbued
with Kantism have made against the Scholastics. Modernism asserts
that the logical nexus is "the weakest link" between the mind and
spiritual truth. So that the contest waged in the twelfth century
is renewed in slightly different terms in our own day, the
application of logic to theology being now, as then, the principal
point in dispute.

In every system of logic there is an underlying philosophical
theory, though this is not always formulated in explicit terms. It
is impossible to explain and demonstrate the laws of thought
without falling back on some theory of the nature of mind. For
this reason Catholic philosophers and educators, as well as those
who by their position in the Church are responsible for the purity
of doctrine in Catholic institutions, have recognized that there
is in logic the Catholic and the non-Catholic point of view. Our
objection to a good deal of recent logical literature is not based
on an unfavourable estimate of its scientific quality: what we
object to is the sensism, subjectivism, agnosticism or other
philosophical doctrine, which underlies the logical theories of
the author. Works on logic written by Catholics generally adhere
very closely to the traditional Aristotelean logic of the schools.
Yet that is not the reason why they are approved. They are
approved because they are free from false philosophical
assumptions. In many non-Catholic works on logic the underlying
philosophy is not only erroneous, but subversive of the whole body
of natural spiritual truth which the Catholic Church guards as
carefully as she does the deposit of faith.

WILLIAM TURNER
Transcribed by Tomas Hancil and Joseph P. Thomas


From the Catholic Encyclopedia, copyright (c) 1913 by the
Encyclopedia Press, Inc. Electronic version copyright (c) 1996 by
New Advent, Inc.

Taken from the New Advent Web Page (www.knight.org/advent).

This article is part of the Catholic Encyclopedia Project, an
effort aimed at placing the  entire Catholic Encyclopedia 1913
edition on the World Wide Web. The coordinator is Kevin Knight,
editor of the New Advent Catholic Website. If you would like to
contribute to this  worthwhile project, you can contact him by e-
mail at (knight.org/advent). For  more information please download
the file cathen.txt/.zip.

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