The logical hexagon, co-discovered independently by Blanché and Augustin Sesmat extends the square of opposition to six statements.
Robert Blanché died in 1975. Nine years before, in 1966, he published with Vrin: Structures intellectuelles. Therein, he deals with the logical hexagon. Whereas the logical square or square of Apuleius represents four values: A,E,I,O , the logical hexagon represents six, that is to say, not only A,E,I,O but also two new values: Y and U. It is advisable to read the article: logical hexagon as well what concerns Indian logic. In La Logique et son histoire d' Aristote à Russell, published with Armand Colin in 1970, Robert Blanché, the author of Structures intellectuelles ( Vrin, 1966) mentions that Józef Maria Bocheński speaks of a sort of Indian logical triangle to be compared with the square of Aristotle (or square of Apuleius), in other words with the square of opposition. This logical triangle announces the logical hexagon of Blanché. It seems that with this logical triangle, Indian logic proposes a useful approach to the problem raised by the particular propositions of natural language. If Robert Blanché's logical hexagon is something more complete and therefore more powerful as regards the understanding of the relationship between logic and natural language, it may be that on a highly important point, Indian logic is superior to that logic proceeding from Aristotle.