Seven years before he died, Franklin confided a regret to his friend and fellow naturalist Joseph Banks. “I begin to be almost sorry I was born so soon,” the elderly American wrote, “since I cannot have the happiness of knowing what will be known 100 years hence” (Smyth 9: 74-75). Would knowledge of the future have made Franklin happy? The hundred years that followed Franklin's 1783 letter to Banks would to a large extent render obsolete Franklin's reputation as a natural philosopher. Franklin seems to prefigure modern scientists, meaning people who (unlike him) make a living by working within a specialized branch of science. In his own time, however, he was a philosopher, a person who did not support himself through his work in science and whose wisdom crossed multiple social, intellectual, and political borders. As a natural philosopher, Franklin had authority in all matters, including political ones. That was crucial to his personal fame and to the authority he would bring to the American War for Independence from Great Britain. Yet even during his life, Franklin witnessed transformations in natural philosophy that would, after his death, make it into the professionalized and specialized fields of modern science.

At the start of Franklin's life, natural philosophy belonged to a unified field of philosophy covering all topics; by the end of his life, most of those who studied the sciences no longer thought of themselves as contributing to a field of knowledge that included theology, moral philosophy, and natural philosophy.