Underdetermination

Underdetermination The term underdetermination refers to a broad family of arguments about the relations between theory and evidence. All share the conclusion that evidence is more or less impotent to guide choice between rival theories or hypotheses. In one or other of its guises, underdetermination has probably been the most potent and most pervasive idea driving twentieth-century forms of scepticism and epistemological relativism. It figures prominently in the writing of diverse influential philosophers. It is a complex family of doctrines, each with a different argumentative structure. Most, however, suppose that only the logical consequences of a hypothesis are relevant to its empirical support. This supposition can be challenged.

1 Relevant terminology The thesis of underdetermination involves a set of specific claims about the relations between bodies of evidence or statements about that evidence, on the one hand, and theories, on the other. All forms of that thesis insist that multiple, mutually incompatible, theories can enjoy the same relation to any given body of evidence. Beyond that point of agreement, however, there are more and less ambitious versions of underdetermination. A few terminological preliminaries are in order before we proceed to examine some of them. To facilitate comparison of the various versions of underdetermination, I shall use this vocabulary: e will refer to whatever evidence is in hand; c will refer to relevant rules or criteria for choosing between hypotheses; and I shall further suppose that we are confronted by a single hypothesis h or, more commonly, by a set of rival hypotheses, h1 ; h2 ; : : : ;n (some of which may not have been explicitly formulated). Now, what every version of the thesis of underdetermination shares in common is this claim: that the relevant criteria, c, and available evidence, e, will provide no rational grounds for preferring hi to some (and perhaps not to any) of the rivals to hi . Various versions of the thesis of underdetermination explore its plausibility under various interpretations of c, the criteria of appraisal.

2 Deductive and ampliative underdetermination Hume argued convincingly that one cannot derive a genuinely universal statement from any finite set of its positive instances (see Hume, D. §2). This is surely correct, but what does it entail for the theory of knowledge? One thing it certainly shows is that if the only criteria of theory choice we allow are those of deductive logic, then the rational acceptance of a theory is always underdetermined by any conceivable evidence. Karl Popper explicitly drew this moral fromHume’s work (see Popper, K.R. §2). It explains why Popper resisted the idea that positive belief in a theory could ever be rational. (Belief for Popper, as for Hume, was a matter of ‘animal instinct’.) Most philosophers refuse to follow Popper in supposing that the rules of deductive logic exhaust the epistemic and methodological resources available for the appraisal of hypotheses. They believe that there are various principles of ampliative inference that come into play in the evaluation of hypotheses. The fact that deductive logic underdetermines theory choice leaves open, they insist, the possibility that these other nondeductive principles may guide theory choice unambiguously. One plausible, if simplistic, ampliative rule of theory evaluation is what Carl Hempel called the Nicod criterion (1965). According to this idea, if some h entails a particular observation report, then the truth of that observation report counts as evidence for h; if the observation report is false, then it counts as evidence against h. About a century ago, Henri Poincaré and others stressed the significance of the fact that, through any finite number of points, indefinitely many curves could be drawn. This made clear that indefinitely many alternative hypotheses were compatible with (indeed, deductively entailed by) any given body of data. If one supposes, with the Nicod criterion, that the potential evidence for h consists simply in its observational consequences, then it is clear that indefinitely many different and conflicting hypotheses will share the same evidential instances. If we take the Nicod rule as a criterion for hypothesis evaluation, it follows that, whenever we are confronted with an h enjoying apparent evidential support (that is, having many true positive or entailed instances), we know that there will be indefinitely many incompatible hypotheses possessing those same instances as ‘evidence’ - even if we cannot formulate them. In sum, theory choice is underdetermined by any methodology which countenances all and only the known positive (or otherwise entailed) instances of a hypothesis as confirmatory.

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Nelson Goodman’s new riddles of induction provided concrete illustrations of the point (1965). Consider a hypothesis like ‘all emeralds are green’ and a contrived rival like ‘all emeralds are green before the year 2000 AD and blue thereafter’. If our observations consist entirely of green-appearing emeralds examined before 2000, then both hypotheses can claim all the same positive instances. Prior to the year 2000, the evidence, however extensive, appears impotent to guide choice between them (see Goodman, N. §3; Induction, epistemic issues in). It is important to note that, even if hypothesis choice is underdetermined in this specific sense, that does not entail that every rival to a given h will fare as well as h does. It means, rather, that there will be rivals which will fare as well.

3 Holistic underdetermination (the ‘D-thesis’) Arguments of a very different sort undergird an even more global form of underdetermination. During the 1950s, W.V. Quine revived arguments made earlier in the century by Pierre Duhem (1906) about the inconclusiveness of falsification (see Duhem, P.M.M.; Quine, W.V. §3). Specifically, the Duhem thesis (D-thesis) holds that hypotheses never approach the tribunal of experience singly but only as parts of much larger webs of belief. This must be so, since auxiliary hypotheses are typically needed even to determine what a given hypothesis predicts about experience. Suppose, asks Quine, that the result predicted by a web of such hypotheses turns out to be mistaken? In that case, he maintains, all we have learned is that we have made a mistake somewhere in our body of beliefs but that blame cannot be further localized. Moreover, he insists that we can hang on to any particular hypothesis we like ‘come what may’, since we can always blame any empirical failures of the web on other strands. More precisely, Quine holds that any given h can be maintained in the face of any apparently negative evidence because (he thinks) there will always be some auxiliary that can be legitimately invoked which will bring h into line with whatever we observe. Any h can, with suitable changes elsewhere in our beliefs, be made to explain any evidence. Although Quine and others have repeatedly asserted this thesis to be true, it has never been proven that every apparently refuted hypothesis can be saved in the face of any evidence by invoking a nontrivial auxiliary hypothesis. If, however, this is correct, then we have a much more global sort of underdetermination to contend with. Whereas previous versions of the underdetermination thesis argued that, for any apparently successful h, there will be at least one rival which exhibits the same success, the holistic version of the underdeterminationist thesis seems to say that, given any apparently successful h, all of its rivals can be made to fit the same evidence that supports h, whatever e is. This view appears to entail a thesis of cognitive egalitarianism, namely, that all rival hypotheses can - with sufficient ingenuity - be made to appear equally well supported by whatever evidence is in hand.

4 Undermining underdetermination What Quine’s version of the underdetermination thesis takes for granted, as do virtually all others, is the idea that a hypothesis’ entailed instances are coextensive with its epistemically supporting instances. He is committed to this since he countenances two hypotheses as equally well supported by e provided that both hypotheses entail e. This idea, the Nicod criterion, undergirds the paradoxes of confirmation, the Goodman paradoxes of induction and Quinean underdetermination. Those who are less taken with the underdetermination thesis believe that its identification of entailed consequences with evidentially supporting instances rests on a misunderstanding of how empirical support works. Specifically, it is easy to show both (a) that many entailed instances of an hypothesis lend it no empirical support and (b) that much of the support enjoyed by many hypotheses comes from outside the set of its entailed consequences. As an example of (a), consider the fact that data used to fix the parameters of a hypothesis, by virtue of being built into h itself, cannot then be used as reasons for accepting h, even though (trivially) h entails them. As regards (b), it is virtually a truism that hypotheses can derive evidential support from instances not entailed by those hypotheses. For instance, the information that the last 10,000 crows have been black is evidence for the hypothesis that the next crow I observe will be black, even though that latter hypothesis entails nothing about the 10,000 crows. Equally, probabilistic statements (for example, ‘most humans die before the age of 100’) typically do not entail any specific claim about observed relative frequencies, even though those same relative frequencies can both confirm and disconfirm statistical hypotheses. Even with respect to a nonprobabilistic hypothesis, one can often derive empirical support from evidence which h does not entail but which is entailed by yet more general hypotheses that Routledge Encyclopedia of Philosophy, Version 1.0, London and New York: Routledge (1998)

in turn entail h. Thus, after the Newtonian synthesis, evidence about bodies falling on the face of the earth supports Kepler’s laws, even though Kepler’s laws themselves entail nothing whatever about cases of terrestrial free fall. In sum, the supporting instances for a hypothesis are not coextensive with its entailed instances nor are its undermining instances exclusively those denied by h. Where does this leave the thesis of underdetermination? Because all the advocates of underdetermination have operated with this mistaken notion of empirical support which assimilates support to being a logical consequence of a hypothesis - we do not presently know whether choice of theory is underdetermined by the evidence. While we do know that rival theories may well have the same known empirical consequences, this knowledge seems to be irrelevant to questions of empirical support, since there are ample grounds for denying that empirical consequences and supporting instances amount to the same thing. It should be noted, finally, that virtually all formulations of the thesis of underdetermination presuppose that, in judging whether the available evidence supports a given hypothesis, we must assure ourselves that there is no possible hypothesis which could be equally well supported. The idea that extant hypotheses are being compared (at least implicitly) with all possible rival hypotheses is probably a hyperbolic view of the theory choice situation. Scientists repeatedly point out that the problem generally facing them is finding even one hypothesis that will fit with the available evidence. The philosopher’s penchant for supposing that the function of evidence is to enable one to choose, not merely between extant hypotheses, but between all possible hypotheses is a conceit that could profitably be dispensed with. See also: Confirmation Theory; Crucial experiments; Inductive Inference; Scientific method LARRY LAUDAN

References and further reading Duhem, P. (1906) La théorie physique. Son objet et sa structure, Paris: Chevalier et Rivière; trans. P.P. Wiener, The Aim and Structure of Physical Theory, Princeton, NJ: Princeton University Press, 1954.(One of the earliest attempts to explore the implications of underdetermination for the epistemology of science.) Glymour, C. (1980) Theory and Evidence, Princeton, NJ: Princeton University Press. (A detailed account of the evidence relation in science.) Goodman, N. (1965) Fact, Fiction and Forecast, Indianapolis, IN: Bobbs-Merrill.(A nominalist’s formulation of new challenges to the idea of instance confirmation, discussed in §2.) Grünbaum, A. (1974) Philosophical Problems of Space and Time, Dordrecht: Reidel. (The standard critique of Duhem and Quine’s accounts of underdetermination.) Hempel, C.G. (1965) Aspects of Explanation, New York: Free Press.(The principal formulation and critique of the qualitative theory of confirmation.) Laudan, L. and Leplin, J. (1991) ‘Empirical Equivalence and Underdetermination’, Journal of Philosophy 88: 449-72.(Elaboration of many of the themes discussed here.) Quine, W.V. (1953) From a Logical Point of View, Cambridge, MA: Harvard University Press.(The locus classicus for the ‘Duhem-Quine thesis’, discussed in §3.)

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