FYI, this might shed light on some problems introduced by Russel and Whitehead in Principia Mathematica: http://www.academia.edu/13159243/2015_Pragmatism_the_A_

FYI, this might shed light on some problems introduced by Russel and Whitehead in Principia Mathematica: http://www.academia.edu/13159243/2015_Pragmatism_the_A_Priori_and_Modality_C._I._Lewis_against_Russell_s_Material_Implication http://www.academia.edu/13159243/2015_Pragmatism_the_A_Prior... See also Hempel's raven paradox.