Newton characterizes the reasoning of Principia Mathematica as geometrical. He emulates classical geometry by displaying, in diagrams, the objects of his reasoning and comparisons between them. Examination of Newton’s unpublished texts shows that Newton conceives geometry as the science of measurement. On this view, all measurement ultimately involves the literal juxtaposition—the putting-together in space—of the item to be measured with a measure, whose dimensions serve as the standard of reference, so that all quantity is ultimately related to spatial extension. I (...) use this conception of Newton’s project to explain the organization and proofs of the first theorems of mechanics to appear in the Principia. The placementof Kepler’s rule of areas as the first proposition, and the manner in which Newton proves it, appear natural on the supposition that Newton seeks a measure, in the sense of a moveable spatial quantity, of time. I argue that Newton proceeds in this way so that his reasoning can have the ostensive certainty of geometry. (shrink)

This thesis provides a new analysis of early contributions to the development of the theory of absolute time—the notion that time exists independently of the presence or actions of material bodies and has no material cause. Though popularly attributed to Newton, I argue that this conception of time first appeared in medieval philosophy, as a solution to a peculiar theological problem generated by a widespread misrepresentation of Aristotle. I trace the subsequent evolution of the theory of absolute time through to (...) the seventeenth-century, and argue that Newton, if anything, retreats from a full endorsement of the doctrine. (shrink)