Like much modern fantasy, Philip Pullman’s His Dark Materials series features magical objects. Each book in the trilogy is named after one; the second is The Subtle Knife . This knife looks unremarkable, but when wielded by the right person, it can cut a hole in the world — a portal into an alternate universe. Unfortunately, the portal’s edges also turn out to be a wound in the fabric of reality … and the wound bleeds. Sinister, invisible things leak out, hungry ghosts that prey upon the living. To banish these ghosts, the tear in reality must be closed.

Among early modern Europeans, magic was not only taken seriously but was inseparable from mathematics, science, and religion; all fell under the rubric of philosophy. “In effect, philosophy is an incubator for other disciplines,” David Chalmers, an Australian philosopher and cognitive scientist, wrote in 2022.…