Not only with their non-classical treatment of modality, concept- determination and of different negations Sigwart and Wundt deliver further examples that psychologism in the transition period between traditional and modern logic was able to promote the development of interesting non- classical logical ideas. On the psychologistic soil, e.g., the important non- Aristotelian ideas of the Russian logician Nicolai Vasil 'ev were developed. On the other hand, Wundt with his non-classical calculus of identity has demonstrated that a psychologistic attitude can harmonize with mathematical-algebraic presentations of logic, a symbioses, which was alive already in the works of George Boole [1847, 1854]. If looking at the history of traditional logic and psychologism in logic, it is clear that psychologism establishes no guarantee for the development of interesting non-classical logical approaches. But because of the connection with applications of logic to the analysis of language, terminology and argumentation patterns and to special epistemic and pragmatic components in science and colloquial contexts, psychologism can constitute a fruitful soil for the development of non-classical ideas.In fact, it was not psychologism, what prevented psychologists like Sigwart, Wundt, or Vasil 'ev to go the way to the new logic, but their inability to leave the traditional paradigms of formal logic, their inability to come to precise formal explications of their non-classical logical ideas.³²