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Abstract
The Russian logician Nikolaj Aleksandrovich Vasil’ev today is widely recognized as one of the forerunners of modern non-classical logic. His importance is stated especially for many-valued and paraconsistent logic (compare, e.g., Smirnov 1962, Arruda 1977, Arruda 1984, Priest and Routley 1989). This assessment of the proposed by Vasil’ev non-Aristotelian revolution in logic is based on the pronounced by Vasiljev rejection of the law of excluded middle and of the law of contradiction, explicated in three extensive consecutive papers from 1910 to 1913. A closer examination will show that Vasil’ev’s rejection of the law of excluded middle in his 1910 paper about particular judgements and the stated there law of the excluded fourth should not be interpreted as a transition to many-valued thinking, understood in the sense of modern logic. On the other side, the sketched in the 1912 paper foundations for a imaginary logic and the formulated there rejection of the law of contradiction is based on an in the modern sense non-classical semantic ground: as basic entities for imaginary worlds are considered negative facts, existing independently from correlated positive facts.