In Memorium:

Hugues Leblanc

March 19, 1924 - September 10, 1999

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Hugues Leblanc was 75 when he died of cardiovascular disease at the Casey House Hospice in Rockville, Maryland. He authored eight books, edited and contributed to three more, and wrote over one hundred papers on symbolic logic and the philosophy of logic.

Hugues was one of the most distinguished logicians of the second half of the twentieth century. His contributions to logic were seminal. He was one of the creators of free logic and of truth-value semantics (the substitution interpretation of the quantifiers), and he made important contributions in the development of probabilistic semantics. His wide ranging interests lead him to studies in classical first-order and second-order logic and the theory of types, many-valued logic, and modal, tense, and intuitionist logics, outfitted with both classical and, most novelly, free quantifiers. He was particularly interested in deductive systems, and developed axiomatic, sequent, and tableaux systems. His contributions to the development of modern natural deduction are noteworthy but unsung. He also published works on confirmation and statistical and inductive inference.

When questioned about philosophical motivation, Leblanc would defend truth-value semantics on nominalistic grounds. However, Leblanc was more interested in the pedagogical and heuristic roles of truth-value semantics rather than its ontological import. In introductory logic courses, Leblanc found truth-value semantics to be a useful teaching device enabling students to grasp more easily fundamental semantic concepts, because it abstracted from tedious details in standard, set-theoretic semantics. Standard semantics can be reconstructed from truth-value assignments read as characteristic functions. Further, truth-value semantics serves as a convenient bridge between standard semantics and probabilistic semantics, facilitating comparative study of these semantics. Finally, by using truth-value semantics, Leblanc was led to important insights, for example, regarding the truth functionality of the ramified theory of types, partially validating observations of Wittgenstein's. Use of standard semantics would have obscured the path he saw to these discoveries. Nevertheless, in later years Leblanc expressed some misgivings about truth-value semantics because some of his work, for example in free intuitionist logic, did not receive the recognition that it deserved because it was carried out within truth-value semantics, which is foreign to the semantic practice of many logicians.

Hugues was a citizen of both Canada and the United States. He was born in Quebec in 1924 and lived in Ste-Hyacinth, Quebec, until 1946. He entered the University of Montreal in 1944 and received a Masters degree from there in 1946. He entered Harvard in 1946, and obtained his doctorate in 1948, with W. V. Quine serving as his dissertation advisor. The 1948 Harvard PhD class in logic working under Quine's direction was particularly distinguished, and included, in addition to Hugues, William Craig, Henry Hiz, John Myhill, and Hao Wang.

In 1948, Hugues joined the Philosophy Department at Bryn Mawr College, and served there until 1967 when he moved to Temple University, until his retirement in 1992. From 1973 to 1979, he served as Chair of the Philosophy Department. After leaving Temple, he joined the University of Quebec at Montreal as an adjunct professor. In 1996, Hugues suffered debilitating strokes, and moved to Northern Virginia to be nearer his children. A memorial service was held for Hugues at Bryn Mawr College on October 3, and his children, former wife, colleagues and friends, rose to testify to his importance in their lives. Bryn Mawr College was most appropriate for the service as Hugues, in later years before his disabling strokes, troubled by university politics and an erratic publisher, reported that he would dream of the beauty and tranquility that he had found on the Bryn Mawr campus in his youth. His ashes are buried in Ste. Hyacinthe with his parents.

Hugues was a Fullbright Fellow 1953-54, an Eugenia Chase Fellow 1958-59, and a Guggenheim Fellow 1965-66. He also received the Paul W. Eberman Award and honorary doctorates from the University of Montreal and Dalhousie University and honors from the University of Quebec at Montreal. He was also a member of the Royal Society of Canada, and he held offices in the Association for Symbolic Logic and the Society for Exact Philosophy (SEP).

Hugues was a hard working and persevering logician. Yet he was also a very social person, and he collaborated with more than twenty other logicians. He was helpful to younger logicians in many different ways by, for example, patiently expounding on perplexing terminology in the literature and introducing them to colleagues at meetings. He enjoyed lively conversation and observing others. He was particularly fond of classical music, and Bach and Wagner were amongst his favorites, but he also enjoyed Brubeck occasionally. He would relax after finishing his work for the day reading biographies (Napoleon) and mysteries (Simenon).

Bernard Linsky, President of the SEP, writes that he has long thought of Hugues Leblanc as embodying the spirit of the SEP -- a love of logic with an interest in the non-classical.

Hugues is survived by his three children, Gabrielle Leblanc of Washington, D.C., Suzzane Leblanc of Newton, MA, and Stephen Leblanc of Reston, VA, three sisters, Odette Leblanc, Suzanne Lincourt, and Eliette Achille all of Montreal, Quebec, and his former wife, Virginia Leblanc of Bryn Mawr, PA.

-- Ray Gumb