Philosophers Since Aristotle Have Traditionally Held That Impossibilities Make Up The Nature Of Logic. Sanford Shieh Investigates An Important But Underexplored Break With This Tradition: Frege And Russell Questioned Whether There Really Are Such Things As Possibilities Or Necessities, And Sought The Foundations Of Logic Elsewhere. Sanford Shieh. Previously Issued In Print: 2019. Includes Bibliographical References And Index.