John Venn and Charles L. Dodgson (Lewis Carroll) created systems of logic diagrams capable of representing classes (sets) and their relations in the form of propositions. Each is a proof method for syllogisms, and Carroll's is a sound and complete system. For a large number of sets, Carroll diagrams are easier to draw because of their self-similarity and algorithmic construction. This regularity makes it easier to locate and thereby to erase cells corresponding with classes destroyed by the premises of an (...) argument, a particularly difficult task in Venn diagrams for more than four sets. Carroll diagrams can represent existential propositions easily, so they are capable of clearly representing more complex problems than Venn's system can. Finally, both Carroll and Venn diagrams are maximal, in the sense that no additional logic information like inclusive disjunctions is able to be represented by them. Carroll's logic diagrams and logic trees constitute his visual logic system. (shrink)

E. E. Constance Jones was one of the first women to study philosophy at the University of Cambridge. This paper focuses on her claim from her first major work, Elements of Logic as a Science of Propositions, that each thing has a unique existence. Jones’s claim follows from claims about tropes and haecceities; but, I suggest, it’s not claims about tropes and haecceities that lead her to accept it. Rather, I suggest, it’s claims about what she calls the denomination of (...) names and the quantitiveness of things that lead her to accept it. Her claim that each thing has a unique existence thus fits within her more general views in Elements of Logic. (shrink)