My tasks in this chapter are two-fold: to trace the influence of Descartes on 17th-century philosophy of science in Britain; and to document the fortunes of the method of hypothesis in Britain in the period immediately before Isaac Newton banished hypotheses from natural philosophy. These two tasks are not unrelated. Indeed, if what follows is anywhere near the mark, the two tasks collapse into one, for insofar as British thinkers of the period from 1650 to 1670 see any promise in the hypothetical method, it is because Descartes, by argument and example, enabled them to see it.