Brentano and Hillebrand on Syllogism: Development and Reception of the ‘Idiogenetic’ Theory

"The seventh chapter presents Franz Brentano and Franz Hillebrand’s ‘idiogenetic theory’, a post-scholastic type of syllogistic theory involving acts of judging which were regarded as belonging as such to a special genus (idios genos) of psychical phenomena. The logical traits of the theory were first put forward by Brentano in his Psychologie vom empirischen Standpunkt (1874, first ed.) and then formally presented in Hillebrand’s Die neuen Theorien der kategorischen Schlüsse (1891). The most novel aspect of the theory was that all judgements were restated in existential form as single- membered assertions, or rejections, whose subject and predicate could be simpliciter converted. The proposal provoked numerous reactions. Particularly the last part of Hillebrand’s system, namely the extension about ‘double judgments’ (existential and predicative judgments bound together), was criticized by Husserl and Meinong, among others. But it also received active support from Brentano’s student Anton Marty. In his chapter, Matteo Cosci recalls the Leibnizian antecedent that showed the character of supposition of the existential import holding in the traditional square of oppositions. That assumption was a matter of concern for Brentano, who may have been aware of its formulation (possibly via Leibniz’s Difficultates Quaedam Logicae) in the process of developing his own reform of syllogistic on new, intentionalistic grounds. Aside from its intrinsic merits and originality, Brentano and Hillebrand’s ‘idiogenetic theory’ had a considerable impact in the fields of descriptive psychology, analytic philosophy and early phenomenology towards the end of the century – not to mention its relevance for the great current in logic inaugurated by Kazimierz Twardowski, prominent student of Brentano and the standard-bearer of his reform in Poland at the beginning of the twentieth century.", Introduction, p.7