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Tag Archives: structural realism

Should we call Newton a ‘Structural Realist’?

Kirsten Walsh writes…

At our symposium last week, someone wondered if we can characterise Newton as a ‘structural realist’.  It is certainly anachronistic to attempt to interpret Newton’s epistemic stance in light of the present-day scientific realism debate.  But the sin of anachronism may be forgiven, if it advances our understanding.  So let us see what advantages this interpretation may provide.

Briefly, structural realism is the view that epistemically, a scientist should only commit herself to the mathematical or structural content of her theories, and remain sceptical about the unobservable entities posited by those theories.

To characterise Newton as a structural realist, one might make the following argument:

    P1. Newton is a realist about his theories, but not about his hypotheses.
    P2. Newton’s theories make claims about theoretical structures, whereas his hypotheses make claims about unobservable theoretical entities.
    C. Therefore, Newton is a realist about theoretical structures, but not about unobservable theoretical entities.

Firstly, consider Newton’s hypothesis/theory distinction.  In a previous post I argued that Newton claims that his doctrine of light and colours is a theory, not a hypothesis, for three reasons:

    T1. It is certainly true, because it is supported by (or deduced from) experiment;
    T2. It concerns the physical properties of light, rather than the nature of light; and
    T3. It has testable consequences.

In contrast, he attaches no special epistemic merit to his corpuscular hypothesis because:

    H1. It is not certainly true, because it is not supported by experiment;
    H2. It concerns the nature of light; and
    H3. It has no testable consequences.

T1 and H1 support P1.  They tell us that Newton is a realist about theories because they can be shown to be true on the basis of experiment.  Moreover, he is not a realist about hypotheses because they cannot be shown to be true on the basis of experiment.  This highlights an important feature of Newton’s methodology: Newton is only epistemically committed to those things that are demonstrated experimentally.

T2 and H2 appear to support P2, but only if the ‘entity/structure’ distinction maps onto Newton’s ‘nature/physical properties’ distinction.  Prima facie, it does.  While Newton probably wouldn’t have been comfortable with the entity/structure distinction, the structural realist debate is often framed in terms of the nature/physical properties distinction.  For example, here’s how the Stanford Encyclopedia of Philosophy describes the structural realist position:

    Structural realism is often characterised as the view that scientific theories tell us only about the form or structure of the unobservable world and not about its nature.  This leaves open the question as to whether the natures of things are posited to be unknowable for some reason or eliminated altogether.

So it looks like the argument for characterising Newton as a structural realist is well-supported by Newton’s distinction between theory and hypothesis.  But what do we gain by characterising Newton in this way?

Chris Smeenk recently pointed out to me in an email that the structural realist label identifies a distinctive feature of Newton’s methodology.  Namely, that he is epistemically committed to his abstract mathematical structures.  He is not an instrumentalist about his theories, but neither is he a realist about the nature of the phenomena they describe.  This might shed some light on the optical debate of the early 1670s, for unlike his contemporaries, Newton does not think there is a contradiction in believing that his theory of light is true, while not committing himself to any particular doctrine regarding the nature of light.

Is this a large enough pay-off to warrant the offence of anachronism?  What do you think?

In this brief post, I have only considered Newton’s attitudes to his own theories.  There are other questions to be raised in connection with structural realism, for example, is Newton a structural realist about the history of science?  In other words, what is Newton’s epistemic commitment to the theories of his predecessors?  I shall leave this question for another time.

On another note, we were very pleased with how last week’s symposium went.  We look forward to telling you all about it next Monday.