Thus, then, the nature of terms, or words, is fixed by definition ; a thing for the most part of extreme difficulty, as, from our ignorance of things, and the complexity of the objects comprehended by usage under any term, it can in few cases be done. The arrangement of things is by genera, where the same class of beings agree in a few attributes only ; and by species, where they agree in more ; and these genera and species may be sub ordinate to each other in numerous pairs, the genus immediately above each species being called the proximate genus. And from this ordinary arrangement logicians obtain a ready method of defining from the specific difference, which, though cer tainly much less adequate than those of the mathematicians, is nevertheless very useful. That is to say, the genus and the specific difference is held to constitute the definition of the species. Thus, if the words, 1. animal ; 2. four.footecl ; 3. graminivorous ; and, 4. fleece-bearing ; be the arrangement of certain beings pos sessing life, we should define the first genus from the only character left by the abstraction, namely, that it is a being pos sessing life ; and the first species would be admitted to be well defined by the words four-footed animal (named qua druped); the second, by the words gra. rninivorous quadruped (named cattle); and the third by the words fleece-bearing cattle (named sheep): or we might less conveniently go through the whole series, and call the sheep a fleece-bearing, gra minivorous, four-footed. animal.
Logicians also avail themselves in de. fining, where practicable, of some strik, ing attribute called the essence of a thing. Thus, under the genus, measure, the species, bushel, peck, quartern, &c. are essentially distinguished by the respective magnitudes which are capable of being numerically expressed.
All our knowledge is contained in pro. positions, 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 pro position agree with the nature of things, it is true, if not, it is false. All proposi tions 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 be, with the word not if the proposition be negative.
Propositions which contain either a plu rality of predicates or of subjects, or which manifest a compounded nature in either, have been called compound pro positions. In the first, however, the pro position 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," in cludes the propositions, " John was de parting, and Thomas was departing." And again the proposition, " Water frozen in flakes 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.
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 negative, and so forth. These distinctions are in few cases
useful, and in many tedious, trifling, and deceptive.
Truth is determined either intuitively ; as when the relation between the predi cate and its subject is immediately seen and admitted. So "the whole is equal to all its parts :"—and these simple truths are called axioms Or else it is determined demonstrative ly ; so the proposition, " the opposite angles made by right lines crossing each other are equal," is not intuitive, but re quires to be demonstrated by a succes sion of axioms connected together : Or lastly, it is determined analogically, upon the probability that what has will, in like circumstances, happen 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 tbllowed by similar acts in men ; we found the doctrine of cause and 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.
It is evident that analogical propositions have much less certainty than those of in tuition or demonstration.
Though in our investigations of truth we must necessarily have recourse to ob servations of individual objects and events, as the ground-work of all; yet, in our in ductions, reasonings, proofi, and pro cesses 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 argumenta tion, it will be the endeavour of a wise man to follow the same course as nearly as may be possible. But, from the con fusion arising from the relations of the complicated 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 to show, whether the reasoner does really pursue the course of pure argumentation, or whether lie de ceives himself or others. Logicians have therefore adopted a formal arrangement for each of the steps of comparison, which they call a syllogism; not calculated in deed for the discovery of remote truths from the use and application of the more immediate or intuitive, but well calculated to give regularity to the mind by scien tific discipline, 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 rea sonings of the middle ages is less 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 ; delu sions, which a sound and bold application of their own science, if it could have been dared, would not have confirmed, but overthrown. ' But to return ; the syllogism, consists of three propositions. In the first, called the major proposition, something is pre dicated of a general subject : in the se cond, called the minor, the subject of the major becomes the predicate of a spe cific subject : and in the third, called the conclusion, the predicate of the general subject is applied to the specific. Thus, ..3/(dor. All men are fallible.