 Fisch and Turquette (1966) discovered three crucial pages out of Peirce’s Logic Notebook (1865–1909, Ms  339).[40]  This shows that Peirce’s invention of three-valued sentential logic predates by at least a decade Jan Lukasiewicz’s and Emil Post’s achievements on the same topic. The three pages contain the essential elements of triadic logic and an intriguing passage about Peirce’s motivation behind triadic logic. If we put Peirce’s development of triadic logic in contemporary terms, Peirce seemed to be branching out to non-standard logic. If so, this adventure would be qualitatively different from the other two we have just discussed in the previous sections.