| Cassius Jackson Keyser | |
| Birth Date: | 15 May 1862 |
| Birth Place: | Rawson, Ohio, US |
| Death Place: | New York City, New York, US |
| Nationality: | American |
| Field: | Mathematics |
| Work Institutions: | University of Missouri SUNY New Paltz Washington University in St. Louis Columbia University |
| Alma Mater: | Columbia University |
| Doctoral Students: | Eric Temple Bell, Emil Post[1] |
| Known For: | Foundation of mathematics |
| Spouse: | Ella Maud Crow |
| Thesis Title: | The Plane Geometry of the Point in Point-Space of Four Dimensions |
| Thesis Year: | 1901 |
Cassius Jackson Keyser (15 May 1862 – 8 May 1947) was an American mathematician of pronounced philosophical inclinations.
Keyser's initial higher education was at North West Ohio Normal School (now Ohio Northern University), then became a school teacher and principal. In 1885, he married a fellow student at the Normal School, Ella Maud Crow. He completed a second undergraduate degree, a BSc, at the University of Missouri in 1892. After teaching there, at the New York State Normal School (now SUNY New Paltz), and at Washington University in St. Louis, he enrolled as a graduate student at Columbia University, earning the MA in 1896 and the PhD in 1901. He spent the rest of his career at Columbia, becoming the Adrain Professor of Mathematics (1904–27) and Head of the department (1910–16). He retired in 1927.
Keyser was one of the first Americans to appreciate the new directions in the foundation of mathematics, heralded by the work of Europeans such as Richard Dedekind, Georg Cantor, Giuseppe Peano, Henri Poincaré, David Hilbert, Ernst Zermelo, Bertrand Russell, and A. N. Whitehead. He was also one of the first to appreciate the mathematical and philosophical importance of his fellow American Charles Sanders Peirce. Alfred Korzybski, founder of general semantics, named Keyser as a major influence. While at Columbia, Keyser supervised only two PhDs, but they both proved quite consequential: Eric Temple Bell and the logician Emil Post.
He became a member of the American board of the Hibbert Journal, and made contributions to that and other philosophical journals. Together with the New International Encyclopedia and his Columbia colleague John Dewey, Keyser helped found the American Association of University Professors (AAUP). He was a fellow of the American Academy for the Advancement of Science, and a member of the American Mathematical Society.
. Ivor Grattan-Guinness. The Search for Mathematical Roots, 1870-1940: Logics, Set Theories and the Foundations of Mathematics from Cantor through Russell to Gödel. 2000. Princeton University Press. Princeton, N.J.. 0-691-05857-1.