Tolkien's turning point: Tolkien and the history of tongues
Professionally speaking, Tolkien was a philologist, interested above all in the history and relationships of languages. Personally speaking, he was a self-declared 'niggler', who took immense pains over details. It was a vital moment when he solved a problem, which would have bothered few authors of fantasy, to do with the history and relationship of the languages of Middle-earth. It was this which opened up The Lord of the Rings to its full scale and sweep.