J.R.R. Tolkien’s academic specialty in the historical study of languages was philology.
Philology examines languages through their historical development, written records, grammar, vocabulary, and relationships to other languages. Tolkien trained in classics and English language and literature, then became a leading scholar of Germanic languages, especially Old and Middle English.
His professional expertise strongly influenced his fiction. Tolkien often built languages first or used linguistic relationships to help shape the histories, peoples, and migrations of Middle-earth. The sound patterns and historical layers of his invented languages reflect the methods of a scholar interested in how real languages change.
Philology is sometimes confused with linguistics, which is a broader modern field studying language scientifically. The terms overlap, but philology traditionally places particular emphasis on historical texts and cultural context. Tolkien himself repeatedly described language and mythology as closely connected parts of his creative work.