Christine Ladd-Franklin wrote her PhD on algebraic logic (Ladd 1883) under Charles Sanders Peirce in the early 1880s. At the time her work was widely celebrated for providing a final and complete characterization of the valid Aristotelian syllogisms, although her name and credit from this work later disappeared from standard histories (Russinoff 1999), (Uckelman 2021) (Cook forthcoming). In this talk we examine a distinct part of her logical system that did not receive significant attention, even in her own time -- the modal interpretation she provides for the formal system constructed in her dissertation. We argue that she deserves credit for formulating a system of modal logic much like systems studied today, decades before Lewis published his celebrated work on modal logic.

REFERENCES: 

Cook, R. (forthcoming), “Understanding Christine Ladd-Franklin’s Logic”, Australasian Journal of Formal Logic.  

Ladd, Christine (1883), “On the Algebra of Logic”, in (Peirce 1883): 17 – 71.

Peirce, Charles S. (ed.) (1883), Studies in Logic, Boston: Little, Brown, and Company. 

Russinoff, I. Susan (1999), “The Syllogism’s Final Solution”, Bulletin of Symbolic Logic 5(4): 451 – 469.

Uckelman, Sara (2021), “What Problem did Ladd-Franklin (Think She) Solved?”, Notre Dame Journal of Formal Logic 62(3): 527 – 552.