Alasdair Ian Fenton Urquhart (/ /; born 20 December 1945) is an emeritus Professor of Philosophy at the University of Toronto. He has made contributions to the field of logic, especially non-classical logic. One of his ideas is proving the undecidability of the relevance logic R. He also published papers in theoretical computer science venues, mostly on mathematical logic topics of relevance to computer science.
A native of Scotland, Urquhart received his MA in Philosophy from the University of Edinburgh in 1967, and his Ph.D. from the University of Pittsburgh in 1973 under the supervision of Alan Ross Anderson and Nuel Belnap.
- Temporal Logic (joint author with Nicholas Rescher), Springer Verlag New York and Vienna 1971
- "The Undecidability of Entailment and Relevant Implication." Journal of Symbolic Logic 49(4): 1059-1073 (1984).
- with Stephen A. Cook, "Functional Interpretations of Feasibly constructive Arithmetic", Annals of Pure and Applied Logic, 1993; preliminary version at STOC'89
- "The Complexity of Decision Procedures in Relevance Logic II", Journal of Symbolic Logic, Volume 64, Issue 4 (1999), 1774-1802.
- ""Alasdair Urquhart was born in Scotland in 1945"". Department of Computer Science - University of Toronto. Retrieved 2 April 2010.