The contributions of Lewis Carroll (Charles L. Dodgson, 1832–1898) to logic consist of several pieces published between 1887 and 1899. The Game of Logic (London, 1887) is a book written for young people to teach them to reason logically by solving syllogisms using diagrams and colored counters. His diagrammatic method is a visual logic system that we know now to be sound and complete.

In Symbolic Logic, Part I (London, 1896) Carroll developed two formal methods to solve syllogisms and

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sorites. The first is the Method of Underscoring that is dependent on his idiosyncratic algebraic notation that he called the Method of Subscripts. The second is his Method of Diagrams, which he extended to handle more than three terms (classes), but without providing examples. However, his diagrammatic system is an improvement over that of his contemporary, John Venn, because first, unlike Venn's system, Carroll's can handle existential statements. Second, as A. Macula...