Donald Cary Williams (28 May 1899—16 January 1983) was an American philosopher and a professor at both the University of California Los Angeles and at Harvard University (from 1939 to 1967). He advocated realism in ontology where he is best known for his expression of trope theory as the "Alphabet of Being".
Williams also published a book on the problem of induction, The Ground of Induction (1947), which argued that the reliability of statistical sampling solves Hume's skepticism about induction.
Williams had both Nicholas Wolterstorff and David Lewis as graduate students.