I have not as yet been able to discover the reason for these properties of gravity from phenomena, and I do not feign hypotheses… It is enough that gravity does really exist and acts according to the laws I have explained, and that it abundantly serves to account for all the motions of celestial bodies.
as a response to those who challenged him to provide causes of gravity. He said, “Hypotheses non fingo,” or, “I feign no hypothesis,” or if you will, “I haven’t even a guess.”
Earlier in a letter he wrote:
That one body may act upon another at a distance through a vacuum without the mediation of anything else, by and through which their action and force may be conveyed from one another, is to me so great an absurdity that, I believe, no man who has in philosophic matters a competent faculty of thinking could ever fall into it.
These passages show that Newton recognized a fundamental causal problem within his theory: that although his mathematics described gravitational physics, it did not provide a causal explanation. It was not until General Relativity 200 years later was this problem solved.
Recently another major fundamental theory of science has been accused of lacking the proper causal structure: Fodor & Piatelli-Palmarini’s attack on evolution, What Darwin Got Wrong. Consider what Fodor says in his recent reply to Block and Kitcher,
A mere chronicle of instances of adaptation would not therefore amount to a theory of adaptation. It would just be “natural history.” We haven’t the slightest doubt that Darwin thought that he had discovered a theory of adaptation. It was, to be sure, a pretty thin theory, as it would have to be in order to apply to evolving creatures as such, whatever their phenotypes and whatever their ecologies.
He is saying that evolution is a mere chronicle of natural history — not a cause of it — just as Newton’s gravitation described gravity without revealing its causal structure. Later he says,
[Biologists should] give up on the project of finding a mechanism for evolution and study the fixation of adaptive traits case by case. Since all the evidence suggests that they are extremely heterogeneous, this should keep evolutionary biologists busy well into the indefinite future.
This means that biologists should give up on repairing evolution and just try to explain individual phenomena moving forward, just as physics moved forward even as Newton knew his theory was on metaphysical shaky ground.
Hence it is Fodor now saying, “Hypotheses non fingo,” because he believes he can describe natural history accurately, but also has no guess as to what caused things to work out the way they did.
* * * * *
In light of this analysis, consider this statement from Block and Kitcher’s counter argument:
After our critique, Fodor and Piattelli-Palmarini have apparently decided that the crucial point is the lack of a “theory” of natural selection. But, as we have noted here, nobody needs a “theory” of the type they demand.
And this from Sober’s recent review [pdf]:
What is the net gravitational force now acting on the earth? That depends on the mass of the sun, the moon, the stars, and of everything else. It does not follow that there are no laws of gravity, only that the laws need to have numerous placeholders. FP may object to my analogy because it is always the mass of these various objects and their distance from the earth that are relevant to the gravitational force that the earth experiences. My reply is that this makes no difference…
Neither has understood the argument as presented above. If Block and Kitcher had understood, then they would have recognized that yes, for the vast majority of people, the “‘theory’ of the type they demand” is unnecessary, but it is, nevertheless, of critical importance to the likes of Newton and Einstein. If Sober had understood, then he wouldn’t have used the worst possible example to make his point: by saying it is “always the mass of these various objects and their distance from the earth that are relevant,” and not mentioning motion, we know he was only thinking about Newtonian Mechanics.
* * * * *
Should we, with Fodor, believe that we are stuck in a philosophical absurdity?
No. What I said in my original criticism of Fodor, found in What Fodor Got Wrong (18 March 09), still applies. Though the above description of the problem is likely clearer than my analysis based on his claims that Natural Selection is statistical and that the struggle for survival is only a metaphor, the problem of causal structure is the same. My solution focuses on using individual struggles as local interactions of Natural Selection — like a gravitational field in General Relativity — and hence provides the causal structure that Fodor wanted.
[EDIT 6 April 2010: I’m thinking I gave Fodor too much credit in this post. I now think his arguments amount to saying that for each instance of evolution we have, we are merely relaying natural history, not a causal explanation. The argument I attributed to Fodor above says that evolution by natural selection is natural history. Fodor must be more agnostic about evolution’s ontology because of how he says it is possible to look for some alternative to natural selection in his reply to Block and Kitcher. My solution is still viable though: since I provide causal structure, this also provides how to describe evolution in a causal way.]