Jon, List, Again, you have not cited any statements by Peirce after June 1911. Therefore, nothing in your note contradicts the evidence that the 1911 version of EGs is Peirce's best and last available version. Furthermore, Peirce's letters of Sept. and Dec. 1911 explicitly reject the version of 1906 on which R669 is based. That does not mean that every statement he wrote about EGs prior to 1911 is obsolete, but it means that everything he wrote prior to June 1911 must be evaluated in terms of his 1911 version. Finally, an enormous amount of research on, with, and about logic has been done during the century following Peirce. The claim that a "sign of illation" is important or even useful for inference is false. The most efficient theorem proving methods today do *not* depend on a sign for if-then. I suggested slides 11 and 12 of http://jfsowa.com/talks/egintro.pdf in my previous note. For further evidence why a sign for if-then can be an *impediment* to inference, please read the slides about Gentzen's method of natural deduction and Peirce's *improvement* on it. For more detail, see the various references, especially http://jfsowa.com/talks/ppe.pdf . By demoting the scroll to *nothing but* a nest of two negations, Peirce's methods are a major simplification and clarification of Gentzen's system. Also note that Frege's proof procedure, which is the basis for the Principia by Whitehead and Russell, puts the sign for if-then at the center. But that results in a horribly complex proof procedure: 43 steps to prove a theorem that takes 7 steps by Peirce's rules (which depend only on negations). There is much more to say about all these issues. But the main point is very clear: In June 1911, Peirce realized that all inferences depend on inserting or erasing graphs or parts of a graph in positive or negative areas. That's is the foundation for defining an open-ended variety of derived rules of inference -- modus ponens is just one of many. Aristotle's syllogisms are others. So are Gentzen's methods and many versions used in computer systems. John
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