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SECTION VII. 

 FEOM 1846 TO 1855. 



< IN the year 1846,' Mr. De Morgan wrote, ' I had begun to 

 collect various matters which had suggested themselves at 

 different times, connected with the theory of the Syllogism lo s ism 

 in Logic.' In the year 1847 the Formal Logic was published. 



The memoirs On the Syllogism, Nos. I., II., III., IV., 

 and V., are Mathematical workings of the principles 

 developed in the Formal Logic] and the tracts On the 

 Structure of the Syllogism, and On the Application of the 

 Theory of Probabilities to Questions of Argument and 

 Authority, immediately preceded it. 



The first chapter of Formal Logic consists, with a few 

 alterations, of the tract entitled First Notions of Logic 

 preparatory to the Study of Geometry ; London, 1839. The 

 work as a whole, and in its higher parts, is original, but 

 the author has been careful to distinguish between what 

 he claimed as exclusively his own and the work of others 

 by printing in italics, in the Table of Contents, the head- 

 ings of those articles which refer to his peculiar system. 

 A reference to this table will show how large and essential 

 a portion was claimed as entirely new. After working 

 these points out in his own mind, the author found that 

 he was able to explain by their means passages of Aristotle 

 till then obscure to himself as well as to others. The 

 two principal features of his own system were the intro- 

 duction of contraries or contradictories, and the idea of 

 definite quantity, into the syllogism. Where all, none, or 

 some had been the utmost quantification employed before, 



