1846. Theory of the Syllogism

‘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 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 headings 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.