Robert Armstrong Pratt, 80, a Chaucer scholar and University of Pennsylvania professor emeritus, died Sept. 11, 1987 at Martha's Vineyard Hospital. A former resident of Haverford, he lived in Chilmark on the island.

A former professor of English at Penn, he was honored for his study of Geoffrey Chaucer. His research into the life and work of the 14th-century English poet brought him two Guggenheim Fellowships and a fellowship at Oxford University and at the Institute for Advanced Study at Princeton University.

The author of dozens of articles published by professional journals on Chaucer and his world, he was co-author of Source and Analogues of Chaucer's Canterbury Tales, published in 1941. He edited a new edition of The Canterbury Tales for publication in 1975.

Born in Bellows Falls, Vt., he grew up in Greenfield, Mass., and attended Deerfield Academy. He earned his degrees, including his doctorate, at Yale University. He also studied in Italy as an exchange fellow at the University of Florence.

He taught at the University of Rochester, Queens College, the University of North Carolina and the University of Illinois before joining Penn's faculty in 1961. He taught at the university for 15 years and retired with professor emeritus status in 1975.

He was a former general editor of the Riverside Chaucer.

Surviving are his wife, Nathalie Rodgers Pratt; daughters, Deborah Macy Borst and Susan Pratt Lanpher; a son, James Rodgers Pratt, and two grandchildren.