LOGIC. 



from their similitude, under classes more 

 or less abstracted as to their modes, cull- 

 ing- these classes by the names of genera 

 and species. And in the names of things, 

 we shall have not only to regard this ar- 

 rangement, but likewise the appropria- 

 tion and correct use of the denomination 

 itself. If we had terms for all simple 

 ideas, and were to enumerate in due or- 

 der all the simple ideas subsisting in a 

 thing, that enumeration would constitute 

 what is called a definition of the thing ; 

 and simple ideas would be, as in strictness 

 they are, undefinable. But since all our 

 sensations are complex, the relations of 

 simple ideas with regard to each other, as 

 residing 1 in the same subject, will afford 

 the means of indicating them. Thus, 

 light is that by which the organ of vision 

 is acted upon, and the word is therefore 

 defined or indicated from that organ Co- 

 lour is a mode of light perhaps too sim- 

 ple to be defined, but clearly indicable 

 from any natural subject in which it may 

 subsist ; as, for example, green is the co- 

 lour of grass, red is the colour of a rose, 

 and yt-llow the colour of an orange. 



Thus, the.n, 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 usoge 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. Tims, if 

 the words. 1. animal ; 2. four-tooted ; 

 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 

 wo v ds four-footed animal (named qua- 

 druped) ; the second, by the words gra 

 nv'nivorous quadruped (named cattle) ; 

 and Hie. 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, moiv, which is called the subjt-ct ; 

 is which is called the copula; and w/#, 

 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 snoiv, 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 : 



