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Short project on the proof theory of Aristotelian syllogisms inspired by a paper by Vaughn R. Pratt

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Aristotelian logic

This short project is inspired by avbop's "Syllogisms" repository, my implementation of propositional and predicate logic, and a paper titled "The four essential Aristotelian syllogisms, via substitution and symmetry" by Vaughn R. Pratt: http://boole.stanford.edu/pub/nemhaj.pdf.

avbop's "Syllogisms" repository can be found here: https://github.com/avbop/syllogisms/. Their method correctly reduces 18/24 valid syllogisms, while this method correctly reduces all 24.

Pratt points out that obversion, conversion, and contraposition can be used as edges to form two connected graphs of valid syllogisms, that this allows us to think of one syllogism as being "reduced" to another, and claims that this is the central desired property of a proof theory. Here I implement his descriptions of obversion, conversion, and contraposition of syllogisms to check that all valid syllogisms eventually reduce to one of four chosen as end points, and that no invalid syllogisms do.

Moreover, this script can easily be adapted to check what subsets of syllogisms may be used as endpoints to reduce any other set of syllogisms. In agreement with figure 1 in Pratt's article above, any of the fifteen syllogisms displayed on the first graph can be used to reduce the other fourteen, while any of the nine syllogisms displayed on the second graph can be used to reduce the other eight, all without validating any invalid syllogisms.

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Short project on the proof theory of Aristotelian syllogisms inspired by a paper by Vaughn R. Pratt

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