Looking twice at the history of science

Thursday, March 14, 2013

Saving the symmetry principle, I: two fallacies

Vanessa Heggie has posted a clear, visible summary of what she rightly calls a “core principle” for historians of science, namely the “symmetry principle.” So this is a great opportunity for me to explain why I disagree with much that my fellow historians of science have written on this topic. Behind the symmetry principle there is an insight that is true, important and worth keeping. But we need to save this insight from the ideas that are often associated with it, many of which I think we should reject. Expand post.


  1. I notice you've skirted carefully around the Pilate/Kuhn question, whether there is any such thing as scientific truth. It pops up a bit in the comments to Heggie's post, vis-a-vis general relativity vs. the inverse-square-law theory of gravity.

    Kuhn notably claimed that general relativity is philosophically more akin to Aristotle's physics than to Newtonian gravity. (Not just the action-at-a-distance issue, either.)

    I look forward to your next post in the series. For my money, the strongest argument for the symmetry principle is simple intellectual curiosity.

    1. Yes, Vanessa's suggestion that Newton might have been wrong about something seems to have inspired more comments than her discussion of the symmetry principle.

      However, to be fair on the comment-writers, it was not very clear from Vanessa's post (at least to me) whether she thought there was an intimate link between the symmetry principle on the one hand and the question of whether science aims at the truth on the other.

      This seems to me a salutary lesson in the importance of making clear distinctions when discussing delicate things in public, even if the distinctions seem esoteric. I'll expand on this in my next post.

  2. As I understood Vanessa's symmetry principle, we should not skip the question why X believed in Y, if we nowadays think EITHER that Y is true OR that the evidence for it is good. What she criticized is the habit of skipping the inquiry and jumping to the seemingly bizarre statements and beliefs trying to understand them.

    I disagree with her in that I would not call that behavior whiggish, it's rather standard. To try to understand why Leibniz thought Newton was wrong is not whiggish. Whiggish, IMHO, is the habit of skipping the bizarre and incommensurable (for example, Leibniz's views on Newton) and making a pompous narrative of progress out of the remaining statements that are understandable from current perspective.

    1. Hi Joachim, and thanks for your comment.

      "We should not skip the question why X believed in Y, if we nowadays think EITHER that Y is true OR that the evidence for it is good."

      Here you have distinguished between the actual truth-value of Y (as currently understood) and the actual evidence for it (as currently understood). The point of the above post was instead to distinguish between truth and evidence as candidate answers to the question why X believed in Y.

      My worry about Vanessa's post is that it emphasised truth as an explanation of past scientist's beliefs, and then conflated truth and evidence. The problem with this is that very few historians or popular authors have supposed that Newton (or anyone else) believed Y just because he thought that Y was true.

    2. Vanessa wrote: "No one believes something simply because it is true; this is a core tenet of the modern history of science"

      That is not emphasizing truth as an explanation of past scientific beliefs but the contrary. Hence I cannot see the basic disagreement between you and her. Your distinction between truth and good evidence is okay, but where is the relevance to the symmetry principle.

      Vanessa's claim seems to be a bit like, don't just take Darwin for granted, ask why he believed the things he did believe and you may yet learn something interesting and possibly find he believed in evolution by natural selection for other reasons than us.

      Now you can rephrase that as "believed in the truth of evolution" or "believed that the evidence for evolution was overwhelming," it does not seem to make a difference in respect to the symmetry principle: ask questions about what you take for granted as much as about what you take for falsified.

    3. I totally agree that "No one believes something simply because it is true," if this means "No one believes something to be true simply because they believe it to be true," or "No one believes something to be true simply because it is, in fact, true."

      My point is that this "sets the bar too low," as I put it in the post. That is, I can't recall ever reading a work of history of science--even an old-fashioned Whiggish one--that committed one of these errors. For example, I doubt that anyone has ever explained Darwin's belief in evolution by saying that he "believed in the truth of evolution." (Of course if you have any examples to hand, I would love to see them!)

      I have two further worries about focusing on truth in this way. One is that it exaggerates the errors of past historians of science, and of popular historians of science. Those people may have erred by (for example) giving rational explanations of Newton's beliefs and irrational ones for Leibniz's beliefs. But they have not committed the error of thinking that the truth of Newton's beliefs is a sufficient explanation of his beliefs.

      My second worry is that, as I put it in the post, "by conflating truth and evidence we make the latter look as unimportant as the former in the resolution of debates, whether in the present or the past." This conflation is unfair on those who think that appeals to evidence are a good way of resolving debates in the present. It is also unfair on those (such as internalist historians of science) who think that appeals to evidence played a role in resolving debates in the past.

  3. In response to Joachim:

    I guess it's a question of who is accusing who of what. In the body of the essay, Heggie writes:

    If we forgo our assumption that he believed in his law of gravity because it was true, we will find all sorts of other explanations about why he believed, and Leibniz did not.

    Now, the question is, what is the referent of "our"? After reading the essay again carefully, I really can't tell who Heggie thinks is guilty of this assumption. Possibly the "scientists, science communicators and science fans today" she mentions earlier, but she gives no quotes of actual people saying anything like that.

    The same is true for the interview with Simon Schaffer that she links to. Schaffer imagines someone saying that Newton got it right for all sorts of sensible reasons, while Leibniz got it wrong "because he was German". Schaffer's hypothetical historian gives no other reason why Leibniz disbelieved Newton's theory.

    1. I think everything said about the symmetry principle would remain correct if the terms 'truth' and 'good evidence' were exchanged in Heggie's post as follows:

      "No one believes something simply because it has the best evidence in its favor."

      instead of:

      "No one believes something simply because it is true."

      Nevertheless, comments here, there and elsewhere claims just that they are taking rational decisions based on evidence.

      The attitude claimed by the symmetry principle, however, should be to suspect one's own conviction that something has the best evidence in its favor as a rationalization has been built after the decision in its favor has been taken by faculties other than our rational thinking devices.

      Of course I see and admit the finer points about the difference between truth and good evidence, but these should not be taken as a cheap excuse for not putting one's convictions under the scrutiny that the symmetry principle demands (calling them rational decisions rather than truths or beliefs).

    2. Probably we should continue this after Michael Bycroft posts part III, which I'm guessing will address just this issue.

    3. Yes, and even if a choice was rational in the end, it could probably not harm to forget that for a second and wonder whether other motives are involved below rationalizations.