©The Royal Society/Richard Valencia.

Hypotheses and Newton’s Epistemic Triad

Kirsten Walsh writes…

Over the weekend, I participated in a conference on ‘Newton and his Reception’, at Ghent University.  I presented a paper based on my idea that Newton is working with an ‘epistemic triad’.  I had an excellent audience in Ghent, and received some very helpful feedback, but I’d like to hear what you think…

To begin, what is Newton’s ‘epistemic triad’?

In his published work, Newton often makes statements about his purported method in order to justify his scientific claims.  In these methodological statements, he contrasts things that have strong epistemic credentials with things that lack those credentials.  Consider, for example, these passages from his early papers on optics:

    For what I shall tell concerning them is not an 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 & wthout any suspicion of doubt. (6 February 1672)
    I shall not mingle conjectures with certainties… (6 February 1672)
    To determine by experiments these & such like Queries wch involve the propounded Theory seems the most proper & direct way to a conclusion. (3 April 1673)

What these passages tell us is that Newton is making a distinction between theories, which are certain and experimentally confirmed, hypotheses, which are uncertain and speculative, and queries, which are not certain, but provide the proper means to establish the certainty of theories.  I call this three-way division Newton’s ‘epistemic triad’, and argue that this triad provides the framework for Newton’s methodology.

To support this argument, I defended the following three theses:

Endurance thesis.  There are some general features of Newton’s methodology that don’t change.  These are characterised by the framework of the epistemic triad.

Developmental thesis. There are some particular features of Newton’s methodology that change over time.  These can be characterised as a development of the epistemic triad.

Contextual thesis. There are some particular features of Newton’s methodology that vary with respect to context (namely, mechanics versus optics).  These can be characterised as an adaptation of the epistemic triad to particular contexts.

The developmental and contextual theses are not news to most Newton scholars.  It is commonly accepted that Newton’s methodology changed in important ways over the course of his life, and that there are methodological differences between Principia and Opticks.  The endurance thesis is more problematic, so I made a special effort to show that Newton’s use of hypotheses is more consistent than we think.  I argued that:

  1. In Principia, Newton appears to be working with the same implicit definition of ‘hypothesis’ that he works with in his early optical papers; and
  2. Hypotheses perform similar methodological roles in all of Newton’s natural philosophical work.

I need to do some more work to properly explicate this methodological role.  But, to state it very broadly, Newton temporarily assumes hypotheses, which act as ‘helping premises’ in his inferences from phenomena.  The fact that a statement may appear in Newton’s writing as a hypothesis, and then reappear later in a query, rule of reasoning, or phenomenon, has convinced many Newton scholars that Newton is inconsistent in his use of hypotheses. Against this conviction, I argue that Newton applies the label ‘hypothesis’ to things that perform a particular function, rather than to a particular claim.

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