J.R.R. Tolkien’s academic field at Oxford was philology.
Philology is the historical study of languages and texts, especially through changes in vocabulary, grammar, sound, and written evidence. Tolkien’s work included Old and Middle English, Old Norse, Gothic, Welsh, Finnish, and other languages that informed his scholarship and creative language-making.
He became Rawlinson and Bosworth Professor of Anglo-Saxon at Oxford in 1925 and later Merton Professor of English Language and Literature in 1945. His expertise in language history strongly influenced the realism of his invented languages and the layered histories of Middle-earth’s peoples.
Philology is sometimes confused with modern linguistics, literary criticism, or archaeology. Tolkien’s scholarship could overlap with all of those areas, but philology best identifies the historical language-and-text discipline for which his Oxford career is especially known. His famous essay on Beowulf also reflects this scholarly background.