he 20th century.  And
any philosopher who uses logic, but doesn't refer to Peirce
is probably still in the grip of the disease.

John Sowa

PS:  For a brief overview of the state of logic in 1909, the
year before the Principia Mathematica was published, I recommend
Peirce's manuscript MS 514, to which I added some commentary:

   <A  HREF="http://www.bestweb.net/~sowa/peirce/ms514.htm">http://www.bestweb.net/~sowa/peirce/ms514.htm</A>

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