Page images
PDF
EPUB

Select Books on Metaphysics. Locke's Essay on the Human Understanding, 2 vols. 8vo. and his Conduct of the Understanding, 12 mo. Dr. Beattie's Essay on Truth,

Dr. Reiu's Essays on the Intellectual Powers of Man, sro. Siewart's Elements of the Philosophy of the Human Mind, svo.

810,

CIIAP. II.-LOGIC. 1. LOGIC is the art of reasoning. In order to reason well, it is illecrocary that the nature of our perceptions and ideas, and the notions or conclusions we draw from thein, should be well understood. Logic, therefore, is a science of extensive occupation ; which has its beginning in the constitution of things, and the processes of the human intellect, and its practical termination in the structure, use, and application of language. its objects are no less than the universal acquisition of knowledge, and that mutual cominunication which constitutes a large part of the employment, and is the most distinguisbing character of man.

2. All our knowledge is contained in propositions, and every proposition consists of three parts. Thus in the proposition, * Snow is white," there are three parts or terms, snow, which is called the subject ; is, which is called the copula; and white, which is called the predicate. If the proposition agree with the nature of things it is true, if not it is false. All propositions are reducible to this form, though both the subject and predicate may be expressed by many words ; but the copula will always be some inflexion of the verb to 12, with the word not if the proposition be negative. • 3. Propositions which contain either a plurality of predicates or of subjects, or which manifest a compounded nature in either, have been called compound propositions. In the first, however, the proposition seems merely to be a number of propositions conjoined, &c.; in the latter, the form of words may be considered as forming a definition of the words or terms. Thus, “ John and Thomas departed,". includes the propositions, “ John was departing, and Thomas was departing." And again the proposition, “ Water frozen in Aakes as it falls from the atmosphere

is coloured like the powder of pure dry salt,” is evidently the same proposition as was first given, excepting that it contains a definition of the word snow taken from its formation, and of the word whiteness from a substance of which it is one of the modes.

4. Our limits will not permit us to enter into the form of propositions from which they are denominated copulative, casual, relative, or disjunctive or modal; as where a proposition itself becomes the subject, or positive, or deative, and so forth. These distinctions are in few cases useful, and in many tedious, tvilling, and deceptive. : 5. Truth is determined either intuitively; as when the relation between the predicate and its subject is inmediately seen and admitted. So “ the whole is equal to all its parts:"-mand these simple truths are called asioms :

8. Or use it is determined demonstratively : 80 the proposition, the opposite angles made by right lines crossing ench other are equal," is not intuitive, but requires to be demonstrated by a succession of axioms connected tow gether:

7. Or lastly it is determined analogically ; upon the probability that what .bas happened will, in like circuinstances, bappen again. Thus, upon the probability that bodies will continue to fall to the ground; that violent motion will be followed by heat; that similar inducements or motives will be followed by similar acts in'men ; we found the doctrine of cause anil effect, and establish our knowledge of physical and moral history, so as to give credit to the past, and confidence, in many respects, to the future,

8. It is evident that analogical propositions have much less certainty than those of intuition or demonstration.

9. Though in our investigation of truth we must necessarily have recourse to observations of individual objects and events, as the ground-work of all; yet in our inductions, reasonings, proofs, and processes of instruction, we proceed from generals to individuals. And, as in strict demonstration the subject and predicate of a proposition are connected by a train of axioms, -so in every other argumentation it will be the endeavour of a wise man to follow the same course as nearly as may be possible. But, from the confusion arising from the relations of the com-. plicated objects of social intercourse, and from the rapidity of language with its abridgments and transpositions, so many things are left to be understood that it is not often an easy task 10 show, whether the reasoner does really pursue the course of pure argumentation, or whether he deceives himself or others. Logicians have, iherefore, adopted a founal arrangement for each of the steps of comparison which they call a syllogism; not calculated indeed for the discovery of remot. truths from the use and application of the more immediate or intuitive, but wx:!| calculated to give regularity to the miîd by scientific disa cipline, and to shorten controversy by a clear detection of the component parts of false reasoning. And here, by the way, it may be remarked that the inexplicable disorder of the logical reasonings of the middle ages is leas to be attributed to the nature of their science of reasoning, loaded as it was with needless distinctions, than to their theological and psychological dogmas, and the delusions into which they wandered with regard to the objects called transcendental ; delusions which a sound and bold application of their own science, if it could have been dared, would not have confirmed, but overthrown.

10. But to return; the syllogism consists of three propositions. In the first, called the major proposition, something is predicated of a general subject in the second, called the minor, the subject of the major becomes the predicate of a specific subject : and in the third, called the conclusion, ihe predicate of the general subject is applied to the specific. Thus,

Major. All men are fallible.
Minor. The Pope is a man;
Conclusion. Therefore the Pope is fallible.

11. The major and minor terms are often called the premises, and the minor is sometimes called the argument. The premises are supposed to be intuitive, or at least incontestable, and the conclusion is established upon the axiom, that whatever can be predicated or afirmed of a genus, may also be predicated of every species comprehended under it; and the like of species, and the individuals comprehended under them.

12. It is usual to denominate the two subjects, and the predicate, terms of the syllogism. The generic word or sentence is called the middle term; its predicate is the major term; and the specific word or sentence is called the minor term. Thus, in the preceding syllogişin the three terins are

Major torm. Fallible.
Middle term. All men.
Minor term. The Pope.

13. Here it is not pretended, that all men should, upon every occasion, reason according to the rules of logic, any more than that a writer should, upon all occasions, insert each individual member of a sentence, and leave nothing to be supplied or understood. But as the man who is a sound grammarian can analyze and parse every member of a sentence, and will write with order, precision, and correctness ; so will the logician, who is able to arrange the parts of an argument in mood and figure, be quick in discerning the imperfect, defective, orinadmissible assertions, and will so dispose his own notions and principles, that his proofs shall be conclusive and clear. The works even of mathematical writers would, in many instances, be benefited by this severity of conduct; and there are few, indeed, which might not be rendered more perfect by strict logical examination and correction.

14. Mood and figure are words applied by logical writers to denote the arrangement of the terms of a syllogism. It is done by the use of the letters A, E, I, O, of which A denotes universal affirmative; E, universal negative ; 1, particular affirmative ; and 0, particular negative. But as it would be difficult to retain in the memory the various changes in the order of these letters, if prefixed to the three parts of a syllogism, fourteen artificial words have been formed, of three syllables each, containing the vowels so to be prefixed in the order of the mood to be denoted by each word. The fourteen moods are classed under these different figures, by which terms logicians mean to deuote the particular situation of the middle term, with respect to the major and minor. The first tigure is distinguished by the middle term being the subject of the major, and predicate of the minor proposition, and its four moods are denoted by the words Barbaru, Celarent, Darii, Ferio, The second figure admits of negative conclusions only, the major being always universal, and one of the premises negative. Its moods are Cesare, Camestres, Festino, Baroco. And in the third figure the middle term is the subject of both premises, the minor affirmative, and the conclusion, particular. Its moods are Darapti, Felapton, Disamis, Dutisi, Bocardo, Ferison.

We shall conclude this article by giving some compion terms in logic.

1. Method is analytical or synthetical. Analytical method resolves the compound into its principles, and the whole into its parts. Synthetical method begins with the parts, and leads to a whole, or it puts together the principles and forms a compound.

2. Argumentum ad judicium, an appeal to the common sense of mankind ;--ad fidem, to their faith ;:-ad hominem, to the practices or professed principles of the adversary ;-ad populum, an appeal to the people :-er concesso, when something is proved by means of soine proposition previously conceded ;-ud passiones, an appeal to the passions.

3. Certainty or Truth is of several kinds; there is a mathematical certainty, which admits of demonstration ; a morul certainty, which is derived from testimony ; a physical certainty, derived from the evidence of the senses and the course of nature; and a theological certainty, founded on the doctrines of the Scriptures.

4. Evidence is of different kinds; as the evidence of sense, founded on the perceptions of our senses; the eridence of intuition, on self-evident axioms, as, that the whole is greater than a part, or, every effect is produced by some cause; the evidence of reuson, founded on clear and indubitable deductions from well-founded premises and doctrines; and the evidence of faith, deduced from the testimony of others.

5. Demonstrations ;priori, is when the effect is proved by referring to the cause; - a posteriori, is when the cause is inferred from the effects.

6. Sophistry is reasoning founded on false premises, or on an ambiguity of terms. A Sophism of composition is when we infer that of any thing in an aggregate or com. pounded sense, which is only true in a divided sense. Sophism of division is when we infer any thing in a divided seirse which is only true in a compounded sense. A So

« PreviousContinue »