Inductivism, Naturalism, and Metascientific Theories
In this paper (1) I will argue that, while inductivism as a view concerning scientific theories has been discredited, the (often implicit) criteria for evaluating metascientific theories is in fact primarily inductivist. The very philosophical community that has condemned and eschewed inductivism for scientific theories in fact applies inductivism for its own metascientific theories. While somewhat troubling, matters are compounded for those advocating a naturalist stance toward metascientific theories, since those advocates suggest that there is not (or should not be) a sharp division between scientific theories and metascientific theories..
(Good) scientific theories
I will start with proposed criteria for a good scientific theory:
(1) Extensivity - it correlates a large amount of phenomena.
(2) Fecundity - it stimulates new research.
(3) Predictive/explanatory power - it is testable and passes tests as well as being unifying. .
(4) Simplicity - it consists of as few assumptions, laws, etc. as is needed.
(5) Coherence - it is internally consistent as well as externally consistent with other established observations, laws, theories, etc.
(6) Plasticity - it should be (relatively) easily modifiable to accommodate new information.
(7) Quantifiability? (Without a doubt, theories that are precise and accurate are preferable to those that aren't. If precision and accuracy are a function of quantifiability, then that is a criterion of a good theory, though it is not obvious that quantifiability is necessary. Nonetheless, all other criteria being met, this does seem to be a virtue.)
There might well be other criteria for a good scientific theory, but I believe these seven are uncontroversial. Are these the criteria we would use to evaluate metascientific theories? I believe not, at least not all of these criteria.
What evaluative criteria do we apply to metascientific theories? I will address this by providing an example of a current debate in science, namely the on-going debate about mass extinctions of life on the earth. First I will give a very brief summary of that debate within the scientific community, then suggest how metascientific theories speak to this debate. At that point, I will look at the criteria used to evaluate these rival metascientific theories. Having done that, I will, in the final section of this paper, indicate why I see metascientific theories as essentially inductivist and remark on why this is especially troublesome for advocates of naturalism.
Mass extinctions case study
1. Scientific concerns
Briefly stated, the Nemesis hypothesis is this: A star with an orbit elliptical to the plane of our solar system has come close enough to our solar system every 26 million years so as to disrupt the Oort Cloud, a hypothetical bubble of material enveloping our solar system; the result of this disruption has been that some of this material was deflected toward the inner planets and subsequently, in the forms of asteroids or meteorites, has bombarded the Earth with the resulting impacts causing mass extinctions of life. The most famous victims of one such bombardment were the dinosaurs at the end of the Cretaceous period.
This characterization of the Nemesis hypothesis, as simple as it is, is actually rather complex because it carries with it several other hypotheses. These other hypotheses include the following: (1) there have been mass extinction events (i.e., relatively sudden and widespread extinctions of a large percentage of species) of terrestrial life, (2) there has been a periodicity to these mass extinctions, (3) the periodicity is one of approximately 26 million years, (4) the periodicity has an extra-terrestrial cause, (5) that extra-terrestrial cause is Nemesis, and (6) the mass extinction of life at the Cretaceous-Tertiary, or K/T, boundary (65 million years ago), including the extinction of dinosaurs, was caused by the impact of an extra-terrestrial body (and indirectly caused by Nemesis).
Each hypothesis in this web of hypotheses has been championed and challenged independently of the others. For example, not everyone in the scientific community accepts the impact view with respect to the extinction at the K/T boundary (e.g., Orth, (2) Hallam (3) ). Indeed, not everyone accepts that there was an extinction event at the K/T boundary (Briggs (4) ). Even accepting impact for that particular extinction event does not entail accepting periodicity of extinction events (e.g., Stigler & Wagner (5) ). Similarly, accepting periodicity does not entail accepting a periodicty of 26 million years (e.g., Rampino & Strothers (6) ), nor does it entail acceptance of Nemesis as the cause of periodicity (e.g., Rampino & Strothers, Schwartz & James (7) ).
A sketchy chronology of work with respect to these hypotheses is as follows: In 1977 Fischer & Arthur (8) published a paper postulating a periodicty of mass extinctions of 32 million years. This paper was met with some criticism, but mostly with silence. (Seven years earlier, Digby McLaren, in his presidential address to the Paleontological Society, had suggested impact as the cause of a mass extinction 365 million years ago.) In June 1980, the research team led by Louis Alvarez published its famous paper (9) suggesting an extra-terrestrial impact as the cause of the extinctions at the K/T boundary. The predominant evidence was the pronounced levels of iridium at the boundary. (By the end of 1983, the Alvarez team reported at least 22 sites, scattered around the world, exhibiting the iridium anomoly at the K/T boundary.) The initial Alvarez paper was immediately criticized in terms of its evidence and its conclusions. Challenges included whether the iridium anomoly was a true anomoly, whether it entails an extra-terrestrial cause, where the impact crater is, whether a single catastrophic event could account for late Cretaceous extinctions (which apparently span numbers of centuries).
In early 1984, Raup & Sepkoski (10) announced a periodicity of mass extinctions of 26 million years, based on computer simulations producing a 'best fit' analysis of family extinctions. This analysis was immediately criticized and continues to be. In April 1984 two causes were proposed to account for a 26 million year periodicity. First, Rampino & Strothers as well as Schwartz & James suggested that periodicity is caused by our solar system's oscillation with respect to the galactic plane. Second, both Whitmore & Jackson (11) and Davis, Hut & Muller (12) suggested an unseen companion to our sun. This yet-to-be-found star was baptized 'Nemesis'. In January 1985, Whitmore & Matese (13) offered a third proposal, that the cause of the periodicity is an unseen tenth planet in our solar system, which they dubbed 'Planet X'. Meanwhile, by the beginning of 1985, corroborating evidence for the Alvarez claim of impact included Luck & Turekian's (14) evidence of anomolous levels of osmium isotope ratios at the K/T boundary, Bohor's (15) findings of shocked quartz at the K/T boundary sites, as well as reports of world-wide distribution of iridium anomolies at the K/T boundary. The three proposals - galactic oscillation, a tenth planet, a companion star - all met with criticisms. The galactic oscillation view, while requiring no new or mysterious ontological objects, suffered the fate of not being in sync with the purported mass extinctions. As the solar system bobs up and down relative to the galactic plane, the mass extinctions should have occurred when the solar system was approaching the galactic plane, but that has not happened. The Planet X view received little attention, but suffered the fate of the planet not having been found. This is true as well for Nemesis (i.e., not having been found), but its defenders claim it is less likely that we would have missed a planet in our solar system than a (very likely dim) star which is not within our solar system, but only approaches it enough to have its gravitational field affect the Oort Cloud.
The summer of 1986 brought renewed objection to an extra-terrestrial cause of extinction at the K/T boundary and increased skepticism of an extra-terrestrial cause for any other extinction event. These objections included claims for large-spread volcanism as the causal agent (e.g., Loper (16) ), questions concerning whether there was truly a sudden extinction event at K/T (e.g., Hallam), and a lack of evidence for the K/T impact site (i.e., a crater). At the same time, bits of further evidence - if not corroborating the impact hypothesis and the periodicity hypothesis, then at least being consistent with them - included the discovery of an impact crater off the coast of Nova Scotia, dated at 200 million years ago. By the end of 1988, the impact hypothesis had gained more adherents, especially with respect to impact at the K/T boundary. Nevertheless, proponents of terrestrial mechanisms for extinction pointed to data that did not fit the impact (or periodicity) view. An apparent extinction event 92 million years ago contained evidence (such as enhanced levels of scandium and titanium, more characteristic of material from the Earth's upper mantle than from meteorites or asteroids) that was deemed more easily explainable by volcanic activity. In addition paleoclimactic studies seemed to indicate that there was significant cooling of the Earth just prior to the K/T extinction. By early 1989 two additional pieces of evidence bolstered the impact view: McHone & Nieman's (17) isolation of stishovite (having been found only at crater sites and very rare in the Earth's crust) at the K/T boundary, along with Zhao & Bada's (18) discovery of two rare amino acids (alpha-amino-isobutyric acid and racemic isovaline), normally associated with meteorites.
By the early 1990's, no impact site had been conclusively identified as the point of K/T impact, though several had been suggested (and rejected), including sites in Iowa, Cuba and Haiti. By the end of 1992, however, an impact site on the Yucatan peninsula, Chicxulub, had been identified as the K/T impact site and by the end of 1994 was accepted by most investigators as 'the real thing'. On the other hand, the volcanists continued to point not only to the Deccan Traps of India as evidence of volcanic activity as the most likely mechanism of extinctions, but claimed the discovery of vast deposits of volcanic basalts, known as the Siberian Traps, to be further corroboration of their position. In addition, several pieces of evidence claimed by proponents of impact as supporting the impact hypothesis came under challenge, including the claim that a variety of forminifera suddenly became extinct at the K/T boundary. Keller (19) and others argued that they did not suddenly become extinct, but gradually died out.
The upshot of this is that at the end of 1994, none of the various hypotheses associated with 'the Nemesis hypothesis' has been established to the complete satisfaction of the scientific community. The hypotheses that there have been mass extinctions and that there was an extinction event at the K/T boundary enjoy the greatest acceptance by the relevant investigators. Even the hypothesis that the K/T extinction was caused by impact is accepted by a majority of scientists. The hypotheses of periodicity of extinction events and specifically of the specific timing and cause of such periodicity have received far less support and have been treated much more as (more or less promising) speculation.
2. Metascientific concerns
There are, of course, a variety of facets of science which philosophers attend to in the process of analyzing the norms and practices of science. These facets range from the gathering of information (e.g., observation, measurement, experimentation) to organizing such information (e.g., models, theories, paradigms) to accounting for such information (e.g., explanation, prediction, hypothesis testing, reduction). There are numerous ways in which the conduct of the scientific community exhibited these facets and it would be beneficial for philosophers of science to look carefully at these numerous ways. For example, with respect to information gathering and hypothesis formation, a variety of experimental techniques were used, including thought experiments, computer simulation experiments, as well as 'traditional' one-shot case studies. Or, the multiple interpretations, reinterpretations, and apparent invulnerability to falsification of much of the proposed evidence both for and against impact can provide fecund material for both philosophers and sociologists of science. Here, however, I want to focus on the issues of theory evaluation and change/progress in science. How, especially since the 1980 Alvarez article, has the scientific community dealt with the Nemesis hypothesis (and its attendent hypotheses of impact, periodicity, etc.)? Has the scientific community acted in ways that have been captured adequately by models proposed by philosophers of science (e.g., Kuhn)? If not, and if these proposed models are meant prescriptively, has the scientific community acted 'irrationally' or in ways that could be aided by such models? I will address these questions by concentrating on the model proposed by Kuhn. (20)
Kuhnian language and characterizations often are used by scientific commentators, including those who have dealt with the Nemesis hypothesis (e.g., Glen (21) , Muller (22) ). That is, they often characterize the activities of the scientific community in Kuhnian terms. Can we properly do so? I think not. While certain features of this history fit Kuhn's model, there are other telling features that do not. First, despite the claims by various scientists (e.g., Gould (23) , Hsu (24) ) that the controversy over Nemesis and impact arose because it represented a neo-catastrophist challenge to the reigning uniformitarian paradigm, it is difficult if not impossible to show that the pre-Alvarez work was substantially different than the post-Alvarez work. 'Normal science' did not change, nor has there been a 'gestalt switch' in which data and phenomema are now incommersurable with pre-Alvarez claims and assumptions. Indeed, advocates on both sides of the various hypotheses point to the same evidence, the same analytic techniques, etc. to make their case. Much of the 'standard paradigm', if there is one, of practicing paleontologists has remained untouched, for example, a commitment to plate tectonics. It certainly is the case that, with a strong advocacy for volcanism alongside with the strong advocacy for impact, there is no dominant paradigm at present. Nor could one make a strong case that the paleontological community is in a period of crisis; there still is widespread consensus on what questions are important to pursue and what techniques are to be followed. Few proponents of impact have been deterred from their view by the presence of apparently inconsistent or even falsifying data (e.g., evidence for the gradual decline and extinction of species prior to the K/T boundary). Nor have many proponents of volcanism been deterred from their view by the presence of apparently inconsistent or falsifying data (e.g., stichovite and shocked quartz at crater sites). Changes that are occurring in the scientific community are not the result of dramatic, sudden gestalt switches even though a gradual acceptance of catastrophism seems to be taking place and is a significant conceptual change.
Metascientific inductivism and Naturalism
How, in practice, do we decide whether or not, say, Kuhn's theory of scientific change is a good theory? I want to claim that basically we look at specific cases or episodes in the history of science to see if they match Kuhn's theory, in much the way I have tried to illustrate with the mass extinctions case above. We don't seem to demand of metascientific theories, say, predictability or fecundity or the various other criteria which we demand of scientific theories. Instead, we look to see, for example, did the plate tectonics revolution fit Kuhn's view (or Laudan's or...)? Or, did the modern synthesis of evolutionary theory and genetics fit Kuhn's view, etc.? Our appraisals of these metascientific theories apparently involve looking for descriptive cases which help to support the metascientific theory or not, a position remarkably like inductivism. I, at least, have seen nothing along the lines of asking what the Kuhnian theory would predict will happen in the mass extinctions debates or propose some strategy for how such debates will or should be conducted (i.e., we haven't demanded fecundity of Kuhn's view). Yes, of course, we insist on internal consistency within a metascientific theory, but when push comes to shove, what really seems to matter is: did Kuhn get it right descriptively (and descriptively, always with respect to the past).
Assuming that what I have said here is correct, one might object that it is quite inappropriate to demand the same evaluative criteria for metascientific theories as we do for scientific theories. Philosophy, after all, is not science, so why evaluate it according to criteria reserved for science? My point here is not to answer that question directly, but to insist that such an objection should not be available to proponents of naturalism, to which I now turn.
It is not clear to me whether naturalism should be conceived as a theory, a stance, an approach, a commitment, or yet even something else. As Barry Stroud (25) recently said in an APA President's Address: "'Naturalism' seems to me...rather like 'World Peace.' Almost everyone swears allegiance to it, and is willing to march under its banner. But disputes can still break out about what it is appropriate or acceptable to do in the name of that slogan." Nevertheless, he sees two basic aspects (or, perhaps, versions) of naturalism, first, an ontological aspect ("a view of what is so, or the way things are, or what there is in the world") and, second, a methodological (or epistemic) aspect ("a way of studying or investigating what there is in the world").
Alex Rosenberg (26) characterizes naturalism in philosophy via four features: (1) The repudiation of 'first philosophy'. (Epistemology is not to be treated as a propaedeutic to the acquisition of further knowledge.); (2) Scientism. (The sciences are to be the guide to epistemology and metaphysics.); (3) Darwinism. (To a large extent Darwinian theory is to be both the model of scientific theorizing and the guide to philosophical theory because it maximally combines relevance to human affairs and well-foundedness.); (4) Progressivity. (Arguments from the history or sociology of science to the non-rationality, or non-cumulativity, or non-progressive character of science, are either unsound or invalid.)
And, of course, the locus classicus , for epistemic naturalism at least, is Quine (27) : "With Dewey I hold that knowledge, mind and meaning are part of the same world that they have to do with, and that they are to be studied in the same empirical spirit that animates natural science. There is no place for a prior philosophy."
My point, I assume, is obvious. If we take a naturalist stand, then the division between scientific theories and metascientific theories is, at best, a difference of degree and not of kind. There seems to be no obvious reason, then, why evaluative criteria for them should be (very) different. What criteria should be used to evaluate metascientific theories? My immediate answer is: I don't know. My second answer is: the criteria for evaluating anything is dependent upon the purpose(s) or use(s) of that thing (e.g., what counts as a good spoon depends on the purpose(s) or use(s) of spoons; what counts as a good theory depends upon the purpose(s) or use(s) of theories). So, what is/are the purpose(s) of metascientific theories? Apparently, given how we in fact evaluate metascientific theories, to describe scientific practice. That, it strikes me, is not very satisfactory for philosophy, as it relegates philosophy to a purely parasitic, descriptive role. However, I will not here propose more. My purpose, instead, has only been to suggest that there is a concern to be addressed, a problem to be solved. It should first be decided if this is correct, if there truly is a problem. If there is, I presume a solution will be forthcoming.
(1) An earlier version of this paper was read at the Irish Philosophical Society annual spring conference, February 1997.
(2) C. J. Orth, et al., "An iridium abundance anomoly at the palynological Cretaceous-Tertiary boundary in northern New Mexico" Science 214 (1981): 1341-43.
(3) A. Hallam, "End-Cretaceous mass extinction event: argument for terrestrial causation" Science 238 (1987): 1237-42.
(4) J. C. Briggs, "Mass extinctions: fact or fallacy?" In Glen (see note 23 below). Pages 230-36.
(5) S. M. Stigler & M. J. Wagner. "Response to D. M. Raup and J. J. Sepkoski, Jr., 'Testing for periodicity of extinction'" Science 241 (1988): 96-8.
(6) M. R. Rampino & R .B. Strothers. "Terrestrial mass extinctions, cometary impacts and the Sun's motion perpendicular to the galactic plane" Nature 308 (1984): 709-12.
(7) R. D. Schwartz & P. B. James. "Periodic mass extinctions and the Sun's oscillation about the galactic plane" Nature 308 (1984): 712-13.
(8) A. G. Fischer & M. A. Arthur. "Secular variations in the pelagic realm" In H. E.Cook & P. Enos (eds.) Deep-water Carbonate Environments, Soc. of Econ. Paleontol. and Mineral. Spec. Publ. 25 (1977): 19-50.
(9) L. Alvarez, et al. "Extraterrestrial cause for the Cretaceous-Tertiary extinction" Science 208 (1980): 1095-1108.
(10) D. M. Raup & J. J. Sepkoski. "Periodicity of extinctions in the geologic past" Proceedings of the National Academy of the Sciences 81 (1984): 801-5.
(11) D. P. Whitmire & A. A. Jackson. "Are periodic mass extinctions driven by a distant solar companion?" Nature 308 (1984): 713-15.
(12) M. Davis, P. Hut & R. A. Muller. "Extinction of species by periodic comet showers" Nature 308 (1984): 715-17.
(13) D. P. Whitmire & J. J. Matese. "Periodic comet showers and Comet X" Nature 313 (1985): 36-38.
(14) J. M. Luck & K. K. Turekian. "Osmium-187/Osmium-186 in manganese nodules and the Cretaceous-Tertiary boundary" Science 222 (1983): 613-15.
(15) B. F. Bohor, et al. "Shocked quartz in the Cretaceous-Tertiary boundary clays: evidence for a global distribution" Science 236 (1987): 705-8.
(16) D. E. Loper "Shocked quartz found at the K/T boundary" Eos 69 (1988): 961, 971-2.
(17) J. F. McHone & R. L. Nieman. "K/T boundary stishovite: detection by solid-state nuclear magnetic resonance and power x-ray diffraction" Geological Society of American Abstracts, 1989. A120.
(18) M. Zhao & J. L. Bada. "Extraterrestrial amino acids in Cretaceous-Tertiary boundary sediments at Stevns Klint, Denmark" Nature 339 (1989): 463-65.
(19) G. Keller "Extended Cretaceous/Tertiary boundary extinctions and delayed population changes in planktonic foraminifera from Brazos River, Texas" Paleooceanography 4 (1989): 287-332.
(20) T. Kuhn, The Structure of Scientific Revolutions. (Chicago: University of Chicago Press, 1962).
(21) W. Glen, (ed.) The Mass-Extinction Debates: How Science Works in a Crisis. (Stanford: Standford University Press), 1994.
(22) R. Muller, Nemesis: The Death Star. (NY: Weidenfeld & Nicholson), 1988.
(23) S. J. Gould, "On the mass-extinction debates: an interview with Stephen Jay Gould" In Glen (see note 23). Pages 253-267.
(24) K. J. Hsu, "Uniformitarianism vs catastrophism in the extinction debate" In Glen (see note 23). Pages 217-29.
(25) B. Stroud. "The Charm of Naturalism." Proceedings and Addresses of the American Philosophical Society 70 (Nov. 1996): 43-55.
(26) A. Rosenberg. "A Field Guide to Recent Species of Naturalism." British Journal of the Philosophy of Science 47 (1996): 1-29.
(27) W.V. Quine. "Ontological Relativity." In Ontological Relativity and Other Essays. New York: Columbia University Press, 1969. Page 26.