Newton's Scaffolding: the instrumental roles of his optical hypotheses

Abstract

Early modern experimental philosophers often appear to commit to, and utilise, corpuscular and mechanical hypotheses. This is somewhat mysterious: such hypotheses frequently appear to be simply assumed, odd for a research program which emphasises the careful experimental accumulation of facts. Isaac Newton was one such experimental philosopher, and his optical work is considered a clear example of the experimental method. Focusing on his optical investigations, I identify three roles for hypotheses. Firstly, Newton introduces a hypothesis to explicate his abstract theory. The purpose here is primarily to improve understanding or uptake of the theory. Secondly, he uses a hypothesis as a platform from which to generate some crucial experiments to decide between competing accounts. The purpose here is to suggest experiments in order to bring a dispute to empirical resolution. Thirdly, he uses a hypothesis to suggest an underlying physical cause, which he then operationalises and represents abstractly in his formal theory. The second and third roles are related in that they are both cases of scaffolding: hypotheses provide a temporary platform from which further experimental work and/or theorising can be carried out. In short, the entities and processes included in Newton’s optical hypothesis are not simply assumed hypothetical posits. Rather, they play instrumental roles in Newton’s experimental philosophy.