BOOKS.
THOMSON'S LAWS OF THOUGHT.*
VARIOUS definitions have been given of logic; but pure logic is the art of forming premises and drawing conclusions from them. In this strict sense of the word, truth or falsehood is nothing to the logician. It is his business to see that the major proposition is constructed according to rule—that it really does affirm what it ought to affirm; that the minor is also duly framed—that it is contained in the major; and that the con- clusion is regularly and fairly drawn. The truth or error of the proposi- tions themselves must be discovered by other sciences,—as, for instance, by fossil geology in a question relating to antediluvian remains ; where a logician might detect a flaw in the argument, or an error in conclusion, but he could not tell whether the facts affirmed were true or the deduc- tion false in nature. It is the indistinct perception of this principle that fills many people with a superstitious idea of the powers of logic. On the other hand, the pedantry, the playfulness, or the dishonesty of many logicians, has brought the art into disrepute, especially when exer- cised upon subjects where the logician was ill-informed, or stupidly un- scrupulous; as they have given rise to ridiculous stories, like the "horse chestnut" and " the chestnut horse."
Even professors of the science have rarely expounded its true charac- ter, or been able to keep the middle path of security. Some, limiting logic to the formation of propositions and the arrangement of syllogisms, have produced books, or rather skeletons, so uncouth and barbarous that they seem altogether useless; being repulsive and almost unintelligible to the tyro, and not required by the proficient. Other writers, extending logic beyond its strict character, have aimed at forming and expand- ing the perception and judgment by the principles of ontology and metaphysics : and such books are popularly useful; but they are logic and something more. A few persons, feeling the barrenness, and for direct purposes of knOwledge the uselessness of logic, have expanded their books by histories of logic and disquisitions on logicians, or by treatises on subjects upon which the logical art is most likely to be employed.
Mr. Thomson seems to have a very just idea of his subject and the manner in which it should be treated. The Outline of the Necessary Laws of Thought is not an account of mere formulae and the abstruse rules on which those formulae are founded. Neither does it attempt to pass beyond the boundaries of logic to inform men on matters in which logic may be exercised, or even directly to train the mind in the art of observing or acquiring. The perception will indeed be improved by the student of Mr. Thomson's section on Conceptions, as the judg- ment will be sharpened by his section on Judgment ; for these subjects are handled as well as syllogisms and reasoning, but they are handled logically. The student is taught how to classify his conceptions—to arrange his " notions" into adequate and inadequate, and so forth : in the section on Judgment he is directed to see whether two such notions agree or disagree, whether they "can or cannot be reconciled" ; and the different kinds of judgments as well as of notions are unfolded. By these processes the mind is trained and sharpened to acquire knowledge ; but knowledge is not directly imparted, because it is logical truth, not natural truth, that is the object in view : for " though the truth or falsehood of a judgment, and consequently its value, depend upon its correctly representing things without us, rather than thoughts within ne, it is primarily concerned with those representations in the mind by means of which alone things are brought into the arena of thought, whether as single objects or as the ground of abstract and general notions."
The proper merit of this book, then, consists in the true perception of the real nature of logic, and the steadiness with which Mr. Thomson brings everything to the test of the preUxistent type in nature itself as exhibited in the mental action. This has enabled him to simplify the study of the art, and to render it more attractive, by showing the principles or laws on which its rules rest, and to render the formulae as intelligible as they probably can be made unless the whole nomenclature were remodel- led. There are also some weaknesses in the book; which, it strikes us, arise from a deviation from nature and reason in favour of prescription— from the use of forms of syllogism which are in some sense useless, as they may be resolved into other and more efficient forms, or from the adoption of examples which though they truly illustrate the class of syllogism are not free from a sophisticated or trifling air, if some of them are not absolutely false. It is indeed necessary to present all sorts of syllogisms to the student; that he may be able to detect ex convert them • but it might be an improvement, in a new edition, to present all formal and subordinate matter in a smaller type.
Besides logic proper, the book contains some sections of a more general kind. The fourth part, on Applied Logic, exhibits its practical exercise in the most complicated subjects; though it also, we fear, shows how useless the mere science is unless combined with actual knowledge and mother-wit. The introduction, on language and the province of logic, is a very able exposition of both subjects, as well as a fitting preparation for the treatise. The following passage will give an idea of Mr. Thom- son's treatment of such general subjects. "Every process has laws, known or unknown, according to which it must take place. A consciousness of them is so far from being necessary to the process; that we cannot discover what they are except by analyzing the results it has left us. Poems must have been written before Horace could compose an ' Art of Poetry,' which required the analysis and judicious criticism of works already m existence. Men poured out burning speeches and kindled their own emotions in the hearer's breast, before an art of rhetoric could be constructed. They tilled the ground, crossed the river or the sea, healed their sicknesses with medicinal plants, before agriculture, chemistry, navigation, and medicine, had become sci- ences. And wherever our knowledge of the laws of any process has become more complete and accurate,—as in astronomy, by the substitution of the Copernican for the Ptolemaic system; in history, by a wiser estimate than our fathers had the means of forming of modern civilization and its tendencies; in chemistry, by * An Outline of the Necessary Laws of Thought ; a Treatise on Pure and Applied. Logic. By William. Thomson, M.A., Fellow and Tutor of Queen's College, Oxford.. Second edition, mach enlarged. Published by Pickering. such discoveries as, the atomic theory and tbe wonders of electro-magnetism,—our progress has been made, not by mere poring in the closet over the rules already known, to revise and correct them by their own light, but by coming back again and again to the process as it went on in nature, to apply our rules to facts, and see how far they contradicted or fell short of explaining them. Astronomers turned to the stars, where the laws they sought for were day and night fulfilling themselves before their eyes ; historians collected facts from the records of differ- ent coin-dries, watched men of many races, of various climates, differently helped or hindered, for there, they knew, the true principles of history were to be read and chemists, in the laboratory, untwisted the very fibres of matter, and watched its every pulse and change, to come &tithe laws which underlaid them. 'Even geometry, says the great chemist Justus Liebig, had its foundation laid in ex- periments and observations; most of its theorems had been seen in practical ex- amples before the science was established by abstract reasoning. Thus, that the square of the hypotbenuse of a right-angled triangle is equal to the sum of the squares of the other two sides, was an experimental discovery, or why did the discoverer sacrifice a hecatomb when he made out its proof?' "The same applies to logic, or the science of the laws of thought. The pro- cess of thought commenced long before the rules to which it adheres with unfail- ing strictness had been drawn out. And though they do not depend on experi- ence—e. e. their truth may be tried and made manifest without recurring to ex- amples—still without experience, without the power of watching our own thoughts and those of others, there could never have been a science of logic; which had its origin when some reflective mind, that had for years performed the various acts of thought spontaneously, began to lay down the laws on which they take place, or to give rules for repeating them at pleasure."
In like manner, to reason to much purpose after logic has been dis- covered, something more than logic is wanted. "In many subjects we do not hesitate from two or three cases of a given pro- perty to infer at once that it will be found in all like cases: when, for example, we observe two or three times that a stone dropped from the mast of a ship in motion falls at the foot of the mast and not behind it, we find in these few trials full evidence (fulgor quidam, mends assensum rapiena) of the operation of some general law, and desist from our experiments, with the conviction that if they were a thousand times repeated the result would be invariably the same. We do not indeed omit to ascertain the reason of the result we have obtained, and should endeavour to find among the known mechanical laws some that would ex- plain it: and if it proved inconsistent with any law of the. truth of which we were already convinced, probably we should suspect the accuracy of our observa- tions, and seek occasion to repeat them with a view to their rectification. But still we should be pretty, certain to hasten to a general statement, believed at first with hesitation, but after many trials with certainty, from a number of cases wholly insufficient in themselves to warrant it. This power of divination, this sagacity, which is the mother of all science, we may call anticipation. The in- tellect, with a doglike instinct, will not hunt until it has found the scent. It must have some presage of the result before it will turn its energies to its attain- ment. "The system of anatomy which has immortalized the name of Oken, is the consequence of a flash of anticipation which glanced through his mind when he picked up in a chance walk the skull of a deer, bleached by the weather, and ex- claimed after a glance, It is a vertebral column !' When Newton saw the apple fall, the anticipatory question flashed into his mind Why do not the heavenly bodies fall like this apple?' In neither case had accident any important share; Newton and Oken were both prepared by the deepest previous study to seize upon the unimportant fact offered to them, and show how important it might become; and if the apple and the deer's skull had been wanting, seine other falling body, or Seine other skull, would, have touched the string so ready to vibrate. Bat in each Case there was a great atop of anticipation:. Oken thought he saw the type of the whole skeleton in the single vertebra and its modifications; whilst Newton conceived at once that the whole universe was full of bodies tending to fall;—two truths that can scarcely be said to be contained in the little occurrences in con- nexion with which they were first suggested. "A mistaken notion prevails that this rapid anticipation does not belong to the philosophic cast. of mind; that it is precisely what Bacon condemns as the method which hurries on rapidly from the particulars supplied by the senses to the most general axioms, and from them as principles, and their supposed in- disputable truth, derives, and discovers the intermediate axioms.' It is thought that caution, and deliberate examination of every particular we can find, before we allow ourselves to form any conclusion whatever, are the conditions of all sound physical inquiry. There is here a confusion of two distinct things. Scrupulous caution should be exercised before an hypothesis is considered to be proved; and the Istw that we believe to be true should be applied to every fact where it can be supposed to operate, and to every other law with which it might interfere, in order to verify exactly what was at first only a happy conjecture. Bacon meant to complain that this sober process did not always follow the bright thought and brilliant suggestion; and perhaps that the bright thought itself was not suggested in the region of facts but in that of words. t•
"Moreover, though it is true that when the premises are given the conclusion is also conceded by implication, we moat not assume that the premises always precede. In the discovery of truth we have, seen that there is always some pre- sage of the conclusion: in the form of a 'question' or judgment to be proved, it really precedes the premises. Given the premises, the conclusion is always im- plied, and any schoolboy can draw it out; but in most cases the difficulty is to find premises, or (which is the same thing) to find a middle term in which the two terms of the question agree. Though the faculty of doing this is thought to be the sign of a logical mind, it rather denotes inventive than reasoning power. But, as has been observed, the study of any subject and a wide acquaintance with facts concerning it meat have disciplined a natural quickness of invention, before any great dicoveries can be made and secured. it might puzzle an uninstructed person even to make an equilateral triangle • and the employment. of equal circles, of which the three sides would he common radii, and therefore equal, as in the first proposition in Euclid, would be a real discovery, a proof of ingenuity. But the ingenuity lies in bringing in the middle notion of radii of a circle at all, which has no apparent connexion with the problem of making three given sides of a figure equal. When the premises are secured, no one can suppose that any acuteness is requisite to discover the conclusion."
Some readers may still ask, of what use is logic ? By teaching us to reason secundum artem, it prevents us from complicating a subject with needless questions, and saves us from falling into errors of reasoning. In other words, it is more useful for detecting falsehood than for discovering truth. The plain man, though not convinced, may be puzzled by falla- cies which lie cannot answer: the logician not only detects them, but expase.s them in their lurking-holes. The indirect utility of logic is to train the mind to distinctness in perception and accuracy in expression ; but as these can only be acquired by the practice, not by the mere know ledge of the science,-there is the risk, with some minds, of resting on the means. Gibbon did not " lament " that he desisted from the study of mathematics before his "mind was hardened by the habit of rigid de- monstration, so destructive of the finer feelings of moral evidence, which must, however, determine the actions and opinions of our lives." The mere logician is liable to a similar danger. Unless the pupil's mind be
rationalized by an acquaintance with the actual estimate of things—unless be be made a man of this world—the orderly arrangement and lucidity of style that logic properly studied will impart, may degenerate into a formal pedantry of manner and into an absurd or trifling refinement of reasoning. The best sorts of reading to cultivate the sensible frame of mind we speak of, are the letters or memoirs of men engaged in affairs ; avoiding (for this purpose) authors by profession, except, perhaps, the satirists and comic writers.
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