INTRODUCTION. 17 



or grammatical point of view. But grammatical usage 

 readily sanctions the free conversion of adjectives into 

 substantives, and vice versd ; we may avail ourselves of 

 this latitude without in any way prejudging the meta- 

 physical difficulties which may be involved. Here, as 

 throughout this work, I shall devote my attention to 

 truths which I can exhibit in a clear and formal manner, 

 believing that, in the present condition of logical science, 

 this will lead to much greater advantage than discussion 

 upon the metaphysical questions which may underlie any 

 part of the subject. 



Every noun or term denotes an object, and usually im- 

 plies the possession by that object of certain qualities or 

 circumstances common to all the objects denoted. There 

 are certain terms, however, which imply the absence of 

 qualities or circumstances attaching to other objects. It 

 will be convenient to employ a special mode of indicating 

 these negative terms, as they are called. If the general 

 name A denotes an object or class of objects possessing 

 certain defined qualities, then the term Not-A will denote 

 any object which does not possess the whole of those 

 qualities ; in short, Not-A is the sign for anything which 

 differs from A in regard to any one or more of the assigned 

 qualities. If A denote ' transparent object,' Not-A will 

 denote 'not transparent object/ Brevity and facility of 

 writing and reading are of no slight importance in a system 

 of notation, and it will therefore be desirable to substitute 

 for the negative term Not-A a briefer mode of expression. 

 The late Prof, de Morgan represented negative terms by 

 small Roman letters, or sometimes by small italic letters k , 

 and as the latter seem to be highly convenient, I shall use 

 a, b, c, d, e, . . . p, q, r, &c., as the negative terms corre- 

 sponding to A, B, C, D, E, . . . P, Q, K, &c. Thus if A 

 means ' fluid/ a will mean ' not-fluid/ and so on. 



k 'Formal Logic,' p. 38. 

 C 



