Steffen Ducheyne writes …
The research team at Otago has kindly invited me to discuss some of the central ideas of my recent monograph “The main Business of Natural Philosophy”: Isaac Newton’s Natural-Philosophical Methodology. My aim in this and next week’s guest post is not to give a complete overview of my book, but rather to bring some salient features of Newton’s methodology to the fore insofar as they are relevant for the speculative-experimental distinction.
Newton sought to separate hypotheses from demonstrations from within natural or experimental philosophy. This, in my view, adds an interesting dimension to the speculative-experimental distinction, for it shows how the distinction was transformed and introduced in the realm of natural philosophy. Newton’s preoccupation with methodological rigour and his distaste of hypotheses led him to explicate the conditions under which our conclusions about the physical world are to be considered as truthful. In this process, he would develop a highly sophisticated methodological position the kind of which had never been seen before.
Before turning to a discussion of Newton’s methodology proper, however, I would like to say something on how I have approached Newton’s methodology. Oftentimes, Newton’s methodology has been approached as if it was a stable given that remained fixed throughout his natural-philosophical career. In my book I have argued that Newton’s methodological views developed alongside with his natural-philosophical research. In Chapter 5, moreover, I distinguish between four distinct phases in the development of Newton’s methodological thought. Furthermore, although Newton clearly favoured his Principia-style methodology, which sets out to physico-mathematically ‘deduce’ causes from their effects, and considered it as the one to be followed ideally, Newton also relied on different methodologies. For instance, in the demonstrative parts of the Opticks he made use of a mixed mathematics treatment and in its speculative parts he proposed hypotheses to be investigated further. In my monograph I have called attention to important diachronic and synchronic differences in Newton’s methodological thought.
Newton’s first optical paper (1671/2) was not only a scientific debut, he also introduced a new methodological ideal on how knowledge about the empirical world is to be established. That ideal consisted in deducing causes from phenomena with demonstrative certainty. In the unedited version of his first optical paper, Newton stated the following on his theory of the heterogeneity of white light: “For what I shall tell concerning them [i.e. colours] is not a Hypothesis but most rigid consequence, not conjectured by barely inferring ’tis thus because not otherwise or because it satisfies all phænomena […] but evinced by ye mediation of experiments concluding directly & without any suspicion of doubt.” In the same period, he criticized the use of hypotheses in natural philosophy. At this point, important features of Newton’s methodological views were in place: his rejection of hypotheses, his ideal of deducing causes from phenomena, his conviction that by injecting mathematics into natural philosophy the latter could partake in the certainty of the former, his endeavour to draw conclusions from experiments, and his desire to treat of light ‘abstractly’, i.e. without making statements on the nature of light. Yet, as I argue in detail in Chapter 4, Newton’s methodological position was at that point still lacking elaboration and justification. That Newton did not provide much detail on how the heterogeneity of white light is derived from the experimentum crucis illustrates the lack of elaboration that characterized Newton’s early methodological views. In next week’s post I will summarize just how Newton’s methodological views developed from the publication of the first edition of the Principia in 1687.