INTRODUCTION, 



1. THERE is as great diversity among authors in the 

 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 suhject on which writers have availed them- 

 selves of the same language as a means of delivering different 

 ideas. Ethics and jurisprudence are liahle to the remark in 

 common with logic. Almost every writer 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 own peculiar 

 tenets, and sometimes to beg the question in their favour. 



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

 as an inevitable and in some degree a proper result of the 

 imperfect state of those sciences. It is not to be expected that 

 there should be agreement about the definition of anything, 

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

 to select from among all the properties of a thing, those 

 1 which shall be understood to be designated and declared 

 by its name ; and the properties must be well known to us 

 before we can be competent to determine which of them are 

 fittest to be chosen for this purpose. Accordingly, in the case 

 of so complex an aggregation of particulars as are compre- 

 hended in anything which can be called a science, the defini- 

 tion 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 until after an extensive and 

 accurate acquaintance with the details of chemical phenomena, 

 VOL. i. 1 



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