In a scene from the movie Black Robe, a Jesuit missionary tries to persuade a Huron chief to let him teach the tribe to read and write. The chief sees no benefit to this practice of scratching marks on paper until the Jesuit gives him a demonstration. "Tell me something I do not know," he says. The chief thinks for a moment and replies, "My woman's mother died in snow last winter."

The Jesuit writes a sentence and walks a few yards over to his colleague, who glances at it and then says to the chief, "Your mother-in-law died in a snowstorm?" The chief jumps back in alarm. He has just encountered the magical power of writing, which allows knowledge to be transferred in silence through symbols.

Augustine's "Confessions" gives a wonderful glimpse of Saint Ambrose, who had mastered the art of reading silently, without moving his lips. Augustine and his friends would gather to watch this feat, amazed that Ambrose could comprehend and retain the unpronounced words, as if by telepathy. Until the thirteenth century, in fact, very few people could read silently. (Mastery of this practice led to a surge in private prayer: until then, believers viewed both prayer and reading as group activities.)

I recently read a long, at times tedious, but also fascinating study called "The History and Power of Writing," by Henri-Jean Martin, which sets out many examples of writing's impact on the world. Writing was long regarded as a supplement to the more reliable medium of oral communication. Scholars recorded epic poems or lists of facts as an aid to memory, but they rarely used writing to communicate new ideas. Stripped of inflection and facial expression, detached from the sensory surroundings of the campfire or banquet hall, writing seemed a thin, ...