But Tolkien also thought – and this takes us back to the roots of his inventions – that philology could take you back even beyond the ancient texts it studied. He believed that it was possible sometimes to feel one’s way back from words as they survived in later periods to concepts which had long since vanished, but which had surely existed, or else the word would not exist. (…) However fanciful Tolkien’s creation of Middle-Earth was, he did not think he was ENTIRELY making it up. He was ‘reconstructing’, he was harmonizing contradictions in his source-texts, sometimes he was supplying entirely new concepts (like hobbits), but he was also reaching back to an imaginative world which he believed had once really existed, at least in a collective imagination: and for this he had very great deal of admittedly scattered evidence.
~ Tom Shippey: J.R.R. Tolkien. Author of the Century.