On 10/9/2017 2:28 PM, [email protected] wrote:
I never would have guessed that “what we mean by “/not/” is “every proposition would be true if it were.”
That comment can only be true if there is no middle option -- i.e., a stone is either hard or not hard AND there is no possibility of being neither hard nor not hard. From http://www.digitalpeirce.fee.unicamp.br/lane/p-trilan.htm
Charles Peirce was the first logician to define logical operators for a many-valued system of logic.[1] In February 1909, on three pages of a notebook in which he recorded his thoughts on logic (MS 339)
Peirce was probably troubled by that comment himself. Or perhaps somebody who attended the lecture asked a question that caused Peirce to rethink the issue for 3-valued logic. In fact, that question may have puzzled the editors -- and that's why they did not publish the final paragraph in the CP. It's significant that Peirce wrote the Lowell lectures in 1903 but didn't write the truth tables for 3-valued logic until 1909. He may have been thinking about the issue for some time, but hadn't worked out the details. John
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