Kirsten Walsh

. Philosophers and scientists often cite ontic factors when explaining the methods and success of scientific inquiry. That is, the adoption of a method or approach is explained in reference to the kind of system in which the scientist is interested: these are explanations of why scientists do what they do, that appeal to properties of their target systems. We present a framework for understanding such “Opticks to his Principia. Newton’s optical work is largely experiment-driven, while the Principia is primarily mathematical, so usually, each work is taken to exemplify a different kind of science. However, Newton himself often presented them in terms of a largely consistent method. We use our framework to articulate an original and plausible position: that the differences between the Opticks and the Principia are due to the kinds of systems targeted. That is, we provide an ontic-driven explanation of methodological differences. We suspect that ontic factors should have a more prominent role in historical explanations of scientific method and development.

Early modern experimental philosophers often appear to commit to and utilise corpuscular and mechanical hypotheses. This is somewhat mysterious, for such hypotheses frequently appear to be simply assumed, which is 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, Walsh identifies three roles for hypotheses. First, Newton introduces a hypothesis to explicate his abstract theory. The purpose here is primarily to improve understanding or uptake of the theory. Second, 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. Third, 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.