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. Aristotle, the founder of the science,

designates it as "analytic", and the Epicureans 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

The Catholic Encyclopedia, Volume IX

Nihil Obstat, October 1, 1910. Remy Lafort, Censor

Imprimatur. +John M. Farley, Archbishop of New York

The Catholic Encyclopedia: NewAdvent.org