ABSTRACT
“We can add to our knowledge, but we cannot subtract from it.” Arthur Koestler opened his classic historical narrative, The Sleepwalkers (1959, p. 19), with this simple message, and it initially seems like a mere truism. But Koestler's words are deceptively unambiguous. They apply in the nominal case—barring physical destruction or other forms of literal inaccessibility, we can never lose the epistemological advances that have preceded us—but they do not hold in the functional case. As several recently influential observers of science have convincingly argued, human knowledge does not grow by gradual, unrelenting accretion. 1 Science advances in fits and starts, some ideas forming part of a relatively permanent edifice, others achieving an initial popularity before being temporarily abandoned—that is, functionally subtracted from a communal knowledge base—only to return in some slightly altered form.
