When G. K. Chesterton was commissioned to write a book about St. Thomas Aquinas, even his strongest supporters and greatest admirers were a little worried. But they would have been a lot more worried if they had known how he actually wrote the book.
Chesterton had already written acclaimed studies of Robert Browning, William Blake, Charles Dickens, Robert Louis Stevenson, Chaucer, and St. Francis of Assisi. Nonetheless, there was a great deal of anxiety even among Chesterton's admirers when in 1933 he agreed to take on the Angelic Doctor of the Church, the author of the Summa Theologica, St. Thomas Aquinas.
Without consulting any texts whatsoever, Chesterton rapidly dictated about half the book to his secretary, Dorothy Collons. Then he suddenly said to her, “I want you to go to London and get me some books.”
“What books?” asked Dorothy.
“I don't know”, said G. K.
So Dorothy did some research and brought back a stack of books on St. Thomas. G. K. flipped through a couple of books in the stack, took a walk in his garden, and then, without ever referring to the books again, proceeded to dictate the rest of his book to Dorothy.
— Dale Ahlquist (2003). G. K. Chesterton. Ch. 9