Popular psychology springs from the desire of people searching for inspiration and self-improvement in a secular form. This desire accounted for some of the success of the eighteenth-century bestseller Poor Richard's Almanack, through which Benjamin Franklin conveyed proverbs and aphorisms about human nature along with weather reports and other practical information. By the time psychology emerged as a discipline in the 1880s and 1890s, the United States already had a sizeable reading public that readily consumed literature on self-improvement and the "gospel of success," and there was also a strong market for spiritualism and mental healing. Books and articles of popular psychology merged easily into these two streams, one secular and the other metaphysical, because they aimed to provide an understanding of the mind's workings that could be used for either practical self-improvement or for more mystical psychic explorations.

Although psychology detached itself from religion when...