Logic; or, The art of reasoning simplified. With exercises on a variety of interesting topics, to guide and develope the reasoning powers of the youthful inquirer after truth

Front matter

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LOGIC,

Preface

That man is an intelligent creature, or a being capable of receiving intelligence to an indefinite extent, is not only a well known and established fact, but also one which involves the most important consequences. This single attribute of human existence not only elevates man in the scale of being, constitutes him capable of unlimited improvement, and of communicating it to others, but at the same time, as to the discharge of his duties, grants him the privilege to increase not only his respectability, but also his usefulness to the society with which he is connected. Though, on the one hand, it would be impossible duly to appreciate a gift so inestimable, yet on the other, be it remembered, that there is nothing given to man, there is no talent with which he is endued, but what requires cultivation. Not only our corporeal but also our mental faculties, unless they have salutary exercise, are liable to decline. The body for want of it is liable to wane into the most lamentable state of langor and imbecility ; and the mind, for reasons perfectly analogous, through the want of exercising the means, with which we are so abundantly privileged, becomes inert and capable of being not only deceived by others, but also irrevocably injured through our own neglect. It cannot for a single moment be doubted, that man, as a sentient, intelligent being, stands as a candidate for happiness. All men seek it, in one way or the other : a single exception would be a parodox in the history of humanity.

According to the extent precisely of our mental vision, not only happiness on the one hand, is before us, until it prospectively rise into all the excellency of a prize whose value is ineflfable, but also on the other, the risk of losing that at which all, in one way or the other aim, is felt with a vigilant sensibility that constitutes the best guarantee of success. Attention is an important act in the mind of man ; when that is gained much is done, yet not all. Though the prospect of success, from attention, immediately rise above zero in the scale of expectancy, yet more is wanting. An object the most desirable may be proposed, yet information of the means of its attainment may be either wanting, or we are not possessed of the method of so connecting the several parts of that information together, as from thence to deduce a conclusion such, as shall infallibly lead to the attainment of the object desired. Hence man, though capable of intelligence, infallible : but especially is that man fallible, who through want of a/fenf ion, through negXeci of informa-- Hon, and of the method of deriving correct and practical conclusions from the same, is as the field, which though capable of producing grain, wheat, and the most luxuriant fruits, remains, through want of culture, not only barren, but encumbered with the most noxious weeds. And happy indeed would it be, were this mere nega^ tive loss, this simple unproductiveness and sterihty, all ;^happy, in this case, would it he, were we warranted by truth and fact, to consider that this would be all the consequence ; as if man, man to whom so much is given, could be irresponsible, when his responsibility rises precisely in proportion to his intellectual superiority, and the privileges of which it is his indispensable duty to avail him-« self.

It is no pait of our present object to define what happiness is, for which we are all, in one way or the other, candidates ; nor to say, from whence we are principally expecting it ; whether in one, or in many ways. It is suflficient to affirm that we are all waiting for that, which questionless is the very fruition of our being, and whose loss renders it even desirable that that being had never existed^ We are all either expecting it, in an object, purely intellectual, or perhaps we in viewing ourselves as members of a society, from whose interests we are not isolated, contemplate it, at least as to all its minOr sources, divided into diverse branches of secular and civil polity. In each and in all these, and in all the various departments of human life, we are surrounded by various means of artifice and deception, and our security from their subterfuges, and the possibility of our ultimate attainment of intellectual excellency and happiness, entirely depend on the correct and successful culture of the inestimable talent with which we are endued, and th€ attentive and diligent use of the privileges with which we are so highly favored. Truth and Error stand so pre-eminently opposed to each other that nothing more than their simple juxta-position is requisite to indicate their immutable hostility. Truth implies and comprehends that which is of the highest importance to man : and the more accurate and ready our methods of detecting and exposing errors are, the more certain are we of being armed against the most fatal enemies not only to ourselves, but to the human family at large. Truth, one would imagine, is so remote from error, or so totally distinct from it, that every rational being, every one capable of discrimination, could need no Rule, no Art, no System, to assist him to separate the one from the other. Yet the experience, not of a day, nor yet of a life, but the history of centuries past, informs us that nothing is more imperatively needed than such Rule, Art, or System,

However opposite the characters of Truth and Error may be, yet there is no fact in history more important and striking, than that man, notwithstanding his capability of intelligence and information, has not always distinguished the one from, th^ other. The pages of history, the schisms in the church, the divisions in the schools, the countless tomes of controversy, the opposition of counsel at the bar, and the conflicts of party in politics, and even the very wars and bloodshed in which they have too often issued, all rise in voluminous testimony of this serious and melancholy fact. Error, however opposed to Truth, yet nevertheless may be so disguised, so diluted, so presented under the illusions of twilight or so mixed up with what is true, that unless we are possessed of the means to expose the counterfeit, the test to detect the ingredient that vitiates, we are liable to be deceived through semblances the most specious and imposing. Error is not inaptly compared to poison. In the extent of their destruction they may differ ; the latter kills a few bodies, the former its thousand, its myriad souls. *' Poison," observes one, " in its concentrated state, nauseates at once, but diluted it may deceive and destroy a city." Thus error exists, even in the present age, diluted, disguised, throughout the whole of human society, to an extent such, that on no subject, theological, political, philosophical, domestic, or foreign, can we find two men, that in all points agree : yet truth in each subject is only one, whilst error, sophistry, or the mistake of a figure in the calculation, may be multiplied, blended, and distorted to an extent indefinite, proportionate to the opacity in the mental vision, or to the means neglected to point out the fallacy and rectify the whole.

That for ages past Error and Sophistry have imposed their destructive effects on myriads reputed rational, is one proof out of many, of the necessity of an aid, which unassisted nature does not ordinarily bestow. Even in the political department how often may it be observed, that one speaker advocates measures diametrically opposed to the other ; and the address of each perhaps is so plausible, as to gain half the house. Are both right ? Certainly not, perhaps neither, but, at least, half the house is deceived ! and that half, if it prevail, will, on a vital question mislead the nation, and involve it in privaiion and suffering. Are there no means then of analyzing the address that contains the fallacy ; no mode of discovering either the false premises assumed ; or if they are right, of showing that the conclusion does not logically follow from them ? Was there no fallacy, whether of composition, division, or accident, no begging the question, nor of building consequences on a mistaken one ? Impossible ; these, or one or more of them, must have been concealed, possibly even from the speaker himself, in one or the other of these orations. And the question yet remains, is there no means of more frequently and successfully exposing error, which in its whole extent may be justly pronounced to be, the most grievous curse that afflicts humanity.

How does it happen that in matters which immediately affect our secular interest, or touch dishonestly our pocket, we provide laws and a vigilant police to detect the offender, that has practised on us to our injury, the artifices of deception, whilst in a thousand cases

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O PREFACE.,

whose consequences may not be so tangible, yet not less important, we suffer so many that will only take the trouble to think and dress up their theory with plausibility,. to practise on our credulity ? Though any man as a free agent, should have the liberty to think as he pleases, yet that constitutes no reason that another should follow in his wake. Is not this, however, a case general to a very lamentable extent. Could a history of the world be so constructed as to point out, on the one hand, the heresiarchs in the church, the demagogues in politics, or the principal leaders in opinion or party ; and on the other, the multitudes on whose credulity, for want of examination, they have practised ; that history would be lamentably libellous on humanity. Could we allow this history to pass in panoramic vision before us ; could we enter ourselves on the long travel, or penetrate the deep vista of time that it involves ; — could we view the mournful shades that have veiled the truth ; — count the myriad suns that have risen and set without imparting one ray to the benighted mind ; — could we enter into the grave assemblies of the ancients, and view the gloom of error resting on the whole ; — could we count the myriad tongues, the thousand pens that have labored to disseminate its influence, or the countless presses that have groaned beneath its volumes counted by the ton : — if in addition to this, we could take another estimate, and scan or measure the reign, the tyranny of error, not by the year, nor yet by the age, but by the century ; and with alarm discover, that even at present, and under the same insidious guise as ever, it is undermining our interests of every kind ; and that deception in its every form is as sedulously at work now as a thousand years ago ; we should then indeed form some faint idea, faint as to the magnitude of its importance, of the necessity of every aid to enable us and others to inculcate truth on the one hand, with all the force of that argument of which it is so happily susceptible, and to expose, on the other, the common enemy, that has with such artful diguise, imposed on so many myriads of our fellow men, to all the contempt and abhorrence to which its mendacity and deceit so justly entitle it.

On the sacred page, we read, indeed, of the ^^ times of ignonorance.'^ And we are likewise aware that a considerate parent does not expect as much from his infant child, as he does from his mature offspring. *' Of them to whom much is given," however, *' much is required." But we cannot with propriety call this the time of ignorance. Wilful ignorance, indeed, may and does exist ; yet not necessary ignorance. We have not only the means of information at command, but may possess ourselves with the mode of rightly using it, to our own advantage, and to the benefit of the society to which we belong. Can we then possibly take a view of past ages and of the lamentable consequences of ignorance and error on the myriads who are now " minish'd from the sons of men,'* without feeling, without compassion, without philanthropy ? In honor, in compliment toourselves^ we presume that we have not only self-interest, but philanthropy too ; and both are involved in the argument. It is no uncommon case that we knowbest how to secure our neighbor's interest, when we know how to secure our own ; and his being secured, will often promote ours also. We are not, and cannot be, isolated beings : both our own interest and that of others are in one common stake. The success of fallacy through the supineness of times past, the examples of past ages, and the superior privileges of this, our own interest, and those of the thousands with whom we are connected, all rise in proof that our welfare and happines are dependant on, if not identified with, our strenuous exertions. Our whole life is, or ought to be, concerned either in the acquisition of truth, or in the detection of what is contrary to its precepts, to whatever department of life those precepts belong.

Enough no doubt has already been said, for the conviction of every ingenuous and liberal mind relative to the utility and importance of Logic. But to our own remarks on this point, we shall take the liberty to add the following given by Dr. Whately. " If it were inquired what is to be regarded, as the most appropriate intellectual occupation of man, as man, what would be the answer ? The statesman is engaged with political affairs; the soldier with military ; the mathematician with the properties of numbers and magnitudes ; the merchant with commercial concerns, &;c.; but in what are all and each of these employed ; employed, that is as men? for there are many modes of exercising the faculties, mental as well as bodily, which are in great measure common to us with the lower animals. Evidently, in reasoning ; men are all employed in deducing, well or ill, conclusions from premises ; each concerning the subject of his own particular business. If, therefore, it be found that the j)rocess going on daily, in each of so many different minds, is, in any respect the same; and if the principles on which it is conducted can be reduced to a regular system, and if rules can be deduced from that system, for the better conducting of the process, then it cannot be denied that such a system and such rules must be especially vjorthy the attention, not qjf^ the members of this or that profession merely, but of every one who is desirous of possessing a well cultivated mind. To understand the theory of that which is the appropriate intellectual occupation of man in general, and to learn to do that well, which every one will and must do, whether well or ill, may surely be considered as an essential part of a liberal education.

" But many who allow the use of systematic principles in other things, are accustomed to cry up common sense as the sufficient and only safe guide in reasoning. Now, by common sense is meant, an exercise of the judgment unaided by any art or system of rules ; such an exercise as we must necessarily employ in numberless cases of daily occurrence ; in which, having no established principles to guide us, — ^no line of procedure distinctly chalked out, — we must needs act on the best extemporaneous conjectures we can form. He wlio is eminently skilled in doing- this, is said to possess a superior degree of common sense. Bnt that common sense is only our second-best guide; that the rules of art, if judiciously framed, are always desirable when'they can be had, is an assertion, for the truth of which I may appeal to the testimony of mankind in general ; which is so much the more valuable, inasmuch as it may be accounted the testimony of adversaries* For the generality have a strong predilection in favor of common sense,- except in those points in which they respectively possess the knowledge of a system of rules, in which they deride any one who trusts to unaided common sense. A sailor will perhaps, despise the pretensions of medical men, and prefer treating a disease by common sense ; but he would ridicule the proposal of navigating a ship by common sense without regard to the principles of the nautical art. A physician again, will perhaps contemn systems of political economy, of logic or metaphysics, and insist on the superior wisdom of trusting to common sense in such matters, but he would never approve of trusting to common sense in the treatment of diseases. Neither again would the architect recommend a reliance on com~ mon sense alone, in building, nor the musician in music, to the neglect of those systems of rules, which in their respective arts,, have been deduced from scientific reasoning aided by experience. And the induction might be extended to every department of practice. Since, therefore, each gives the preference to unassisted common sense, only in those cases where he himself has nothing else to trust to, and invariably resorts to the rules of art, whenever he possesses the knowledge of them, it is plain that mankind universally bear their testimony, though unconsciously and unwillingly,. to the preferableness of systematic knowledge to conjectural judgment.

" There is, however, abundant room for the employment of common sense in the application of the system. To bring arguments,, out of the form, in which they are expressed in conversation, and in books, into the regular logical shape, must be of course, the business of common sense, aided by practice; for such arguments are, by supposition, not as yet within the province of science ; else they would be already strict syllogisms. To exercise the learner in this operation, I have subjoined, in the appendix, some examples, both of isolated argument, and of the analysis of argumentative works.

" The cause of truth universally, and not least of religious truth, is benefitted by every thing that tends to promote sound reasonings and facilitate the detection of fallacy. The adversaries of our faith would, I am convinced, have been on many occasions, more satisfactorily answered, and would have had fewer openings for cavil,

PREFACE.

had a thorough acquaintance with Logic been a more common qualification than it is. Not only all those who are engaged in or designed for the sacred ministry, but all others who are sensible that the cause of true religion is not a concern of the ministry alone, should remember that this is no time to forego any of the advantages which that cause may derive from an active and judicious cultivation of the faculties. It is not, however, solely or chiefly for polemical purposes that the cultivation of the reasoning faculty is desirable ; in persuading and investigating, in learning or teaching, in all the multitude of cases, in which it is our object to arrive at just conclusions, or to lead others to them, it is most important. A knowledge of logical rules will not indeed supply the want of other knowledge, nor was it even proposed, by any one who really understood the science, to substitute it for any other; but it is no less true that no other can be substituted for it : that it is valuable in every branch of study ; and that it enables us to use the knowledge we possess to the greatest advantage."

We cannot here forbear to mention that it was our privilege to be personally acquainted with one, who, if ever man was, was a master in Logic ; and very fortunately so, for no man, since the seventeenth century was ever more engaged in controversy; and what was the consequence ? It is immediately and every where apparent. The ease with which he, on every occasion, managed his adversary ; the dexterity he displayed in immediately detecting the fallacy, wherever and however concealed ; the facility he evinced in dissipating his illogical conclusions, and the suavity and temper which were prevalent through the whole, left him decidedly, in the estimation of every rational and candid mind, in undisputed possession of the field; — -and why ? — He was an eminent Logician.

But however we would advocate the acquisition of truth, it is by no means our intention to intimate that Logic, or the Art of Reasoning, is the only means by which Truth, in every sense, is discovered. To the representation of Logic as the method of discovering Truth, as if it were the only method ; or even a method, without stating what are those truths we are to expect from the process which Logic institutes, may be in no small degree attributed the misunderstanding of the specific object it proposes. Truths are either those of Information or Instruction. The former we derive from observation or testimony, or even from experiment instituted at the time, by a conjectural conclusion deduced from assumed premises. The latter, truths of Instruction, we derive from data, which though they may be in the possession of others, yet probably have been employed either to no purpose, or misemployed by fallacy and incorrect reasoning, to a wrong one. These data fall within the province of Logic, either from them to deduce a truth not before perceived as a necessary consequence of the premises they afford ; or to detect an error resulting from their misapplication.

*' When it is asked," says Dr. Whately, " whether such great discoveries as have been made in Natural Philosophy, were accomphshed or can be accomplished by Reasoning ? the inquirer should be reminded that the question is ambiguous. It may be answered in the affirmative, if by Reasoning is meant to be included, the assumption of Premises. ^^ To the assumption of premises, frequently scientific men, in search for some new or undiscovered truth, are indebted ; from which, though at first, nothing better than sl probable conjecture can be inferred, yet that conjectural inference may institute a course of experiments, which may ultimately establish the fact. " Thus Sir Humphrey Davy finding that the flame of hydrogen gas was not communicated through a long slender tube, conjectured that a shorter, but still slenderer tube, would answer the same purpose. This led him to try the experiment, in which by successively shortening the tube, and at the same time lessening its bore, he arrived at last at the wiregauze of his safety-lamp." Now throughout the whole of this process, assumed premises^ conjecture, experiment, it is evident that a kind of inductive reasoning was going on, that is, so far as reasoning hypothetically, and in a necessary case, from assumed premises, is acting until positive ones can supply their place ; yet it is not that strictly, in which Logic, that pretends not to the discovery of new Truths in an unrestricted sense, is concerned.

Truths of Information belong to the sciences ; to Theology, Ethics, Jurisprudence, to the Arts, and to the Business and Experience of common life ; and a distinct class of them to each. For the acquisition of these, the sciences, and the several sources respectively to which Truths of Information belong, must be duly consulted. These are the volumes from which we have to cull this kind of intellectual furniture, and nothing else can properly communicate it. It is here too that we not only have to derive our Information, and all the truth which it implies, but, moreover, clear and distinct ideas of each individual, both in its isolated and relative position, without which all our knowledge is vain. The Instructor in Logic takes it for granted that his pupil comes prepared with these, that he has them not to seek, or at least that he is furnished with as mani/ as are necesmry for his immediate purpose.

It is of considerable importance in this early stage of our inquiry, to state distinctly that it is to the sciences, and to the proper sources that we must look for Information ; but it is ihe peculiar province of Logic to teach the most salutary and practical use of the knowledge we possess, either for the purpose of instructitig ourselves or others, by that only argumentative process, which must necessarily, in every rational mind, demand conviction ; or for the refutation of conclusions, whether deduced from irrelevant premises, or falsely derived from true ones ; sophisms which are 00 frequently exemplified by those who are dispossessed of that

^discrimination, and unacquainted with the mode of detecting fallacy which it is the business of Logic to impart.

When we, on first opening the pages of Euclid, read, " a line is length without breadth ;" *' a plane rectilineal angle is the inclination of two straight lines to one another that meet in a point ;" ** that a triangle is a plane figure bounded by three lines," &c. ; from hence we derive Ideas, and Truths of Information ; but it is not the business of Logic to teach us these : these are nothing but the mere furniture, the requisite data, that we must possess, before we can oommence and successfully employ to any beneficial purpose, the argumentative process. But when we are once furnished with the prerequisite terms and premises, and come to read, "If two triangles have two sides, and the included angle in the one, equal two sides and the included angle in the other, the triangles will be equal and identical in all respects," we require the demonstrative or argumentative process ; the result afforded by which is a Truth of Instruction, which it is the province of Reasoning or Logic to establish on premises from which the proof is legitimately derived.

Nothing is more calculated to throw into the shade, if not most unjustly into disrepute, an art or science, than misrepresenting its distinct and specific object; loading it with more than it professes to perform, imputing to it obligations which are either inconsistent with itself, or disreputable in themselves. A time was, when the object of Astronomy was not distinguished from that of Astrology ^ or the pretended art of divining futurities from the configurations and motions of the heavenly bodies. And had not Astronomy been happily rescued from this misconception, and established on the basis of its own independent reputation, it might to the present day, in the estimation of the uninformed, have ranked in a grade equally low with that of palmistry, legerdemain or necromancy. A time existed in which even the respectable science of Chemistry was merged into the mystified shades of Alchemy, whose most popular and ostensible object was to find the secret of turning all things into gold ; or the panacea, the universal cure of all diseases to which humanity is subject, without excepting even mortality itself. Chemistry, however, very fortunately has emerged from this eclipse, and presents itself disencumbered of distortions not its own, in that elegant form in which it is at once so interesting and useful to society.

But who are they, that from want of proper discrimination, have for a period nearly equal to the night of Alchemy, succeeded to throw the shades of misrepresentation on the peculiar and specific object of Logic, and that so artfully, as to convert characters, in other respects of considerable respectability and importance in the Republic of Letters, to their own heresy ? Had these been the mere tyros in the art, those who had contented themselves with merely some hasty glances at an introductory chapter, there would have been nothing in the circumstance uncommon, and they would have verified only the ancient adage, so general in its application, " damnunt quod non intelligunt," they condemn what they do not understand. For the honor of those, however, who have professedly undertaken to teach the art, or to write voluminous treatises.on the science, we could wish that we had it not to say, that the charge

lies exclusively at their door, 2y u o iiS'a'niaM?^ Ka.i rccvra. ov ytvaxruiis, "Art

thou a teacher, and knowest not these things ?" implies a charge equally applicable at present as in former times. Amongst them we could mention one, who has written a volume with no other effect, than to evince the possibility of a man's writing more than 300 pages on a subject, which he, from the first time he took up his pen to the last page it had written, evidently did not understand* To discover a ship at sea, 300 miles from the port whence she had sailed, without any one on board knowing either where they were, or whither they were going, would lead to the inference that neither compass was in the binnacle, nor navigator in the cabin ; but to find a being reputed intellectual, navigating over 300 pages of heterogeneous and irrelevant matter, performing a sort of zig-zag traverse wide of the mark, and having no bearing on the object originally proposed, is merely one example, among the many thousands which might be added, of the danger of following any one, merely because he is a teacher, without the test of our own examination and scrutiny, and the exercise of that function which it is the specific object of Logic itself to develope and explain.

No science can be expected to make any considerable progress^ which instead of being regularly cultivated on right principles, has been liable to the misrepresentation of those who never correctly understood its specific object themselves, nor therefore could teach it to others. From the time of the schoolmen, censured by Bacons rather for their abuse of the art, than for any legitimate purpose to which they applied it, down to the present, we meet with a host of authors, who have either written expressly on the same, or more or less made remarks thereon ; which leads to a discovery no less strange than true, that very few clearly understood the subject ! ! Only two writers, the former about the ^middle of the last century* and the latter. Dr. Whately, have proved that they were aware that Logic is chiefly concerned with the third act of the mind^ ARGUMENTATION ; and with SUCH EXPRESSION OF IT as correctly to convey its conclusiveness to others. These two alone appear to have cleared the equation from the co-efficients with which it was encumbered, from quantities foreign to its distinct intention, and that concealed it in mists of metaphysical irrelevancy.