158 MEMOIR OF AUGUSTUS DE MORGAN. 



1847. the ideas of more or less with their contradictories formed 

 Formal an essential part of the Formal Logic. 



The tract On the Syllogism, &c., read at Cambridge in 

 ^November 1846, excited great interest in the minds of 

 those Logicians who were following out the application of 

 Mathematics to Logic. Dr. Whewell had wished the 

 writer to read it himself, and kindly begged him to visit 

 him at Trinity Lodge for the time. This he was not able 

 to do. I wish it had been practicable for him to mix 

 more freely and frequently with the friends who shared 

 his interests ; but on looking back to the great variety of 

 subjects he treated, and the work he was engaged in at 

 the time, it is evident that this would have been impos- 

 sible. The memoir On the Dispute between Keill and 

 Leibnitz was printed in this year. I hoped, on first con- 

 sidering in what way to mention the Logical works, to be 

 able to supply some of my own deficiencies by inserting 

 the letters which were addressed to him both on the re- 

 ception of the tract and the publication of the volume. 

 But they are too numerous to form a part of this work. 

 I am, however, very thankful to be able to insert here 

 some excellent strictures on that which I dare not myself 

 have attempted to describe the relation of Psychology 

 and Mathematics in my husband's mind. These remarks 

 were kindly given to me by Mr. De Morgan's friend and 

 former pupil, Mr. Cecil Monro: 



Such attention to Logical method is not to be confounded 

 with mere accuracy and explicitness of statement and demon- 

 stration. These are vital qualities, indeed, of Mathematical 

 exposition, qualities which every one sees to be characteristic of 

 Mr. De Morgan's work ; which are, in fact, characteristic of it 

 in an extraordinary degree ; but it is in a more important sense 

 than this that he was at least as great in Logic as in Mathematics. 

 Even in his most strictly Mathematical writings the examination 

 of mental processes is visibly an end in itself, as distinguished 

 from the exhibition of mental products. In its psychological 

 aspect his end is pursued through historical and even bibliogra- 

 phical inquiries, which, independently of their value as informa- 



