The Marlo Diagram in the Classroom

Abstract

In this paper we present some results obtained using the Marlo diagram for the didactic of logic in a High School in Huelva, Spain, between 2014 and 2019. This tool was created by the author to improve the bad results obtained with traditional methods of propositional calculus, excessively complex, abstract and far from common sense. To avoid the most frequent fallacies in the classroom, we developed a simple and intuitive diagrammatic deduction system that allows us to decompose and visualize the simplest and most elementary steps of reasoning. Our goal was reinforcing valid inference patterns by synchronizing natural, formal and diagrammatic languages. Although in 2014 we could only solve syllogisms in our diagram, since 2016 we can also solve propositional logic exercises. This is possible by expressing all logical connectives by quantifying the predicate. Proceeding this way allows us to solve any inference of the propositional calculus in our diagrams through the same processes of analysis and synthesis that take place in the syllogism. The fact of recovering the middle term as the basis for any inference allows us to teach logic from common sense and, consequently, obtain better results in performance tests. The first comparisons we have made of our teaching method with the conventional method encourage us to continue developing a tool that, according to our experience, allows us to improve abstract thinking from an earlier age than conventional methods.