Explicating

Duhem, Popper and Lakatos -- to name but some -- all agreed that Newton was a poor methodologist. My aim is to show that Newton's Principia contained a subtle and complex methodological programme which I endeavour to explicate during my talk. I shall argue that Newton's methodology proceeds in a way more demanding than hypothetico- deductivism. I will focus on Books I and III of Principia. Book I contains an abstract physico-mathematical treatment of -- in principle -- arbitrary centripetal forces. Book I furthermore deals with abstract 'measures' only, i.e. with abstract quasi-physical definientes (e.g., velocity, time, etc.). Book I corresponds to what I call the phase of model construction. Book III properly deals with measurements, i.e. observed definientes, and, accordingly, with real- world forces. Once 'measures' are replaced by concrete measurements, Newton's mathematical models are turned into 'philosophical' models, i.e. into models with referential content. In my analysis of Book I, I shall pay special attention to the Definitions and the Laws of Motion in Principia and to the models' inferential capacity. In my analysis of Book III, I shall highlight the phase of model application, theory formation and theory testing, and I shall explicate the importance of Newton's regulae philosophandi for the phases of theory formation and theory testing. By the end of my talk, I hope to have made clear that the hypothesis that Newton was a poor methodologist is beset with many difficulties.