Nuel D. Belnap, Jr., American Logician and Philosopher, Dies at Age 94

Nuel Dinsmore Belnap, Jr. (1930-2024), American logician and philosopher who made contributions to the philosophy of logic, temporal logic, and structural proof theory—and first cousin four times removed to Gilbert Belnap, died on 12 Jun 2024 at age 94. According to his obituary, in 1963, after a year spent in Belgium on a Fulbright Fellowship, Nuel moved with his family to Pittsburgh, Pennsylvania, where he began his nearly 50-year career at the University of Pittsburgh as a professor. He was the Alan Ross Anderson distinguished professor for philosophy until his retirement. Nuel’s contributions to the philosophy of logic, temporal logic, structural proof theory, and especially his work on the foundations of two very distinct theories of truth, affected generations of students and scholars around the world. An original thinker as well as a generous collaborator, Nuel wrote several books considered definitive on philosophy, logic, and truth. He visited several continents giving lectures and contributing to professional philosophical groups, and received multiple honors and awards, among them a Guggenheim Fellowship and an honorary doctorate from Leipzig University. He was elected to the American Academy of Arts and Sciences in 2008. Regarding his work in logic and philosophy, Anil Gupta, who was a doctoral student of Nuel’s and later his colleague at Pittsburgh, wrote:

Belnap’s contributions to logic and philosophy are broad, deep, and elegant. He was a co-founder (or co-discoverer, depending on one’s philosophy) of the systems E and R of entailment logics, whose study has occupied several generations of logicians and philosophers. He isolated (with Michael Dunn) the truth-functional fragment of entailment logics—a fragment now known as the Belnap-Dunn logic—and provided a powerful motivation for it (in “How a Computer Should Think” and “A Useful Four-Valued Logic”). He was a pioneer in the study of the logic of questions and of the logic of agency in branching time. He generalized the notion of branching times to branching space-times to help us better understand physical as well as mental phenomena. He made an important contribution to proof theory with his Display Logic. He was a co-originator of the prosentential theory of truth, and he helped give birth to the revision theory of truth. (There is nothing odd here, for these two theories of truth are not competitors; they address different issues.) Belnap presented his research in numerous articles and in the following books: The Logic of Questions and Answers (co-authored with Thomas Steel, 1976), Entailment (vol. I, with Anderson, 1975; vol. II, with Anderson and J. M. Dunn, 1992), The Revision Theory of Truth (with A. Gupta, 1993), Facing the Future (with M. Perloff and M. Xu, 2001), and Branching Space-Times (with T. Müller and T. Placek, 2021). . . . Three volumes of essays have been published on Belnap’s work: Truth and Consequences (eds., J. M. Dunn and A. Gupta), New Essays on Belnap-Dunn Logic (eds., H. Omori and H. Wansing), and Nuel Belnap on Indeterminism and Free Action (ed., T. Müller). The last volume appeared in Springer’s Outstanding Contributions in Logic series. . . . Belnap was an outstanding teacher and trained several generations of logicians and philosophers. He had a special talent for making vivid, and thus comprehensible, even the most abstract and complex concepts. What Belnap said once about Alan Anderson applies to him also: his presentations “pleased the sensibilities as well as the intellect.” Belnap was a generous teacher, quick to recognize even the smallest contributions of students. He made students feel that they too could contribute to this imposing enterprise that is logic and philosophy.

Categorised in: Announcements, Obituary

This post was written by Brent J. Belnap