* INTRODUCTION. 



writers on logic have generally understood the term as it was 

 employed by the able author of the Port Koyal Logic ; viz. 

 as equivalent to the Art of Thinking. Nor is this acceptation 

 confined to books, and scientific inquiries. Even in ordinary 

 conversation, the ideas connected with the word Logic include 

 at least precision of language, and accuracy of classification : 

 and we perhaps oftener hear persons speak of a logical arrange 

 ment, or of expressions logically defined, than of conclusions 

 logically deduced from premises. Again, a man is often called 

 a great logician, or a man of powerful logic, not for the accu 

 racy of his deductions, but for the extent of his command 

 over premises ; because the general propositions required for 

 explaining a difficulty or refuting a sophism, copiously and 

 promptly occur to him : because, in short, his knowledge, 

 besides being ample, is well under his command for argumen 

 tative use. Whether, therefore, we conform to the practice of 

 those who have made the subject their particular study, or to 

 that of popular writers and common discourse, the province 

 of logic will include several operations of the intellect not 

 usually considered to fall within the meaning of the terms 

 Reasoning and Argumentation. 



These various operations might be brought within the com 

 pass of the science, and the additional advantage be obtained 

 of a very simple definition, if, by an extension of the term, 

 sanctioned by high authorities, we were to define logic as the 

 science which treats of the operations of the human under 

 standing in the pursuit of truth. For to this ultimate end, 

 naming, classification, definition, and all other operations over 

 which logic has ever claimed jurisdiction, are essentially sub 

 sidiary. They may all be regarded as contrivances for enabling 

 a person to know the truths which are needful to him, and to 

 know them at the precise moment at which they are needful. 

 Other purposes, indeed, are also served by these operations ; 

 for instance, that of imparting our knowledge to others. But, 

 viewed with regard to this purpose, they have never been con 

 sidered as within the province of the logician. The sole object 

 of Logic is the guidance of one s own thoughts : the com 

 munication of those thoughts to others falls under the con- 



