The word ‘environment’ has a history. Before the mid-nineteenth century, the idea of a singular, abstract entity—the organism—interacting with another singular, abstract entity—the environment—was virtually unknown. In this paper I trace how the idea of a plurality of external conditions or circumstances was replaced by the idea of a singular environment. The central figure behind this shift, at least in Anglo-American intellectual life, was the philosopher Herbert Spencer. I examine Spencer’s work from 1840 to 1855, demonstrating that he was exposed (...) to a variety of discussions of the ‘force of circumstances’ in this period, and was decisively influenced by the ideas of Auguste Comte in the years preceding the publication of Principles of psychology (1855). It is this latter work that popularized the word ‘environment’ and the corresponding idea of organism–environment interaction—an idea with important metaphysical and methodological implications. Spencer introduced into the English-speaking world one of our most enduring dichotomies: organism and environment. (shrink)