I have to prepare a response to a couple of papers being given next week at an international conference on "mysticism" -- a fraught term -- and one of the two papers, by Nobuo Kazashi (professor of philosophy at Japan's Kobe University), is titled "The Young William James and Ontological Wonder Sickness."
I've not read James in a long time, so I returned to one of his most famous books, The Will to Believe: And Other Essays in Popular Philosophy, and Human Immortality (Courier Dover Publications, 1956), where James describes what he calls "ontological wonder-sickness":
Our mind is so wedded to the process of seeing an other beside every item of its experience, that when the notion of an absolute datum is presented to it, it goes through its usual procedure and remains pointing at the void beyond, as if in that lay further matter for contemplation. In short, it spins for itself the further positive consideration of a nonentity enveloping the being of its datum; and as that leads nowhere, back recoils the thought toward its datum again. But there is no natural bridge between nonentity and this particular datum, and the thought stands oscillating to and fro, wondering "Why was there anything but nonentity; why just this universal datum and not another?" and finds no end, in wandering mazes lost. Indeed, [a certain Professor] Bain's words [affirming the end of mystery in the complete vision of science when all has been encompassed within the most general of scientific laws] are so untrue that in reflecting men it is just when the attempt to fuse the manifold into a single totality has been most successful, when the conception of the universe as a unique fact is nearest its perfection, that the craving for further explanation, the ontological wonder-sickness, arises in its extremest form. As Schopenhauer says, "The uneasiness which keeps the never-resting clock of metaphysics in motion, is the consciousness that the non-existence of this world is just as possible as its existence." (pages 71-72)In the reference to finding no end but being "in wandering mazes lost," James quotes from Milton's epic Paradise Lost, Book 2.561, where the more philosophical of the fallen angels apparently fall into a type of wonder-sickness -- and James is probably punning between "wandering" and "wondering" -- though Milton does not explicitly state that these erring angels pose the ultimate ontological question. They perhaps don't suffer from James's peculiar illness.
But what is the symptom of "ontological wonder sickness," anyway? The "oscillating to and fro, wondering"? Or the "craving for further explanation" itself? James is not entirely clear on this point.
Be that as it may, I suspect that a fear of nothingness lies at the heart of James's concern, for the Schopenhauer quote emphasizes "that the non-existence of this world is just as possible as its existence."
Perhaps I should ask my friend Bill Vallicella.