A SYSTEM OF LOGIC, 



INTRODUCTION. 



§ 1. There is as great diversity among authors in tlie modes which 

 they have adopted of defining logic, as in their treatment of the details 

 of it. This is what might naturally be expected on any subject on 

 which -writers have availed themselves of the same language, as a means 

 of delivering different ideas. Ethics and jurisprudence are liable to 

 the remark in common with logic. Almost every philosopher having 

 taken a different view of some of the particulars which these branches 

 of knowledge are usually understood to include ; each has so framed 

 his definition as to indicate beforehand his owii peculiar tenets, and 

 Bometimes to beg the question in their favor. 



This diversity is not so much an evil to be complained of, as an in- 

 evitable and in some degree a proper result of the imperfect state of 

 those sciences. There cannot be agreement about the definition of a 

 thing, until there is agreement about the thing itself To define a 

 thing, is to select from among the whole of its properties those which 

 shall be understood to be designated and declared by its name ; and 

 the properties must be very well known to us before we can be com- 

 petent to determine which of them are fittest to be chosen for this pur- 

 pose. Accordingly, in the case of so complex an aggregation of par- 

 ticulars as are comprehended in anything which can be called a science, 

 the definition we set out with is seldom that which a more extensive 

 knowledge of the subject shows to be the most appropriate. Until 

 we know the particulars themselves, we cannot fix upon the most correct 

 and compact mode of circumscribing them by a general description. 

 It was not till after an extensive and accurate acquaintance with the 

 details of chemical phenomena, that it was found possible to frame a 

 rational definition of chemistry ; and the definition of the science of life 

 and organization is still a matter of dispute. So long as the sciences 

 are imperfect, the definitions must partake of their imperfections; and 

 if the former are progi-essive, the latter ought to be ^o too. As much, 

 therefore, as is to be expected from a definition placed at the com- 

 mencement of a subject, is that it should define the scope of our in- 

 quiries : and the definition which I am about to offer of the science of 

 logic, pretends to nothing more, than to be a statement of the question 

 which I have put to myself, and which this book is an attemjit to re- 

 solve. The reader is at hberty to object to it as a definition of logic; 

 but it is at all events a correct definition of the subject of this 

 volume. 



A 



