Doubt

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DOUBT

To be in doubt about a proposition is to withhold assent both from it and from its contradictory. Although people sometimes withhold assent with no reason for doing so and persist in this even after conceding that they have no reason, doubt is rational only when one has a reason for it and reasonable only when the reason is a good one. Doubt may be accompanied by various feelings, but it seems unlikely that there are specific feelings uniquely associated with it; in general, the feelings associated with doubt are anxiety or hesitation, which are identified as feelings of doubt when they arise in contexts involving questions of belief. In any case, philosophers are not ordinarily concerned with psychological characterizations of a doubter's state of mind. Their attention is primarily devoted to understanding the conditions under which doubt is reasonable and to defining the limits of reasonable doubt.

Evidence and Reasonable Doubt

Whether it is reasonable for a person to doubt a proposition cannot always be decided solely by considering the evidence that the person possesses relevant to the proposition or, in a situation in which there is purportedly noninferential knowledge, by considering his ground for assent. Doubts that are unreasonable or absurd in one situation may be quite reasonable in another, although the available evidence or ground is the same in both cases. For example, special caution is appropriate when the penalties for error are particularly great; hence, an ordinarily acceptable basis for assent may be inadequate if much depends upon avoiding error, although the gravity of the risk does not in itself constitute evidence. Moreover, a basis for assent that would be entirely compelling in normal circumstances may be insufficient if otherwise remote possibilities of error must be taken seriously because of threats posed by a resourceful deceiver.

From the fact that someone has no reason to doubt a given proposition, therefore, it does not follow that the evidence he possesses is sufficient to render unreasonable all doubts concerning the proposition. It would seem quite worthwhile to explore the ways in which the reasonableness of doubt is affected by considerations other than the available evidence or ground for assent. Philosophers, however, on the whole, are interested only in very general principles that are not affected by contingencies of any sort. For this reason, perhaps, philosophical studies of doubt have usually been concerned with limiting cases in which the reasonableness of doubt depends only on the available evidence or ground for assent. In other words, they have dealt mainly with what is indubitable —with what it is never reasonable to doubt regardless of contextual variables of the sort described above. Accordingly, a philosopher's designation of certain propositions as dubitable is not generally to be understood as a denial that there are circumstances in which doubting these propositions would be absurd. The designation means only that given the evidence or ground for the propositions, there are conceivable circumstances in which doubt would be reasonable.

Conditions of Indubitability

Toward the end of the First Meditation, René Descartes invokes the distinction between what is indubitable and what, in normal circumstances, is open to no reasonable doubt. In defense of his decision to regard as dubitable many propositions which, in practice, it is unreasonable to doubt, he declares, "I cannot at present yield too much to distrust, since it is not now a question of action but only of meditation and of knowledge." In their usual concerns, individuals are not often required to decide whether a proposition is indubitable, as distinct from deciding whether there is any reason to doubt it. Questions of indubitability are theoretical: they concern only the relation between a proposition and the evidence or ground for it, and take no account of the other concrete circumstances in which a proposition is evaluated.

limits of relevant evidence

When is one entitled to regard a proposition as indubitable? It might be maintained that one is not entitled to do so as long as anything which can serve as evidence relevant to the proposition remains unexamined, on the ground that when this evidence comes to be examined, it may turn out to require an alteration of belief. But by virtue of the empirical and logical connections among facts, the truth-value of any proposition affects the truth-values of an unlimited number of others: Hence, the truth-values of an unlimited number of propositions are relevant to that of any proposition and may serve as evidence concerning it. Since it is impossible to examine each of these other propositions, no proposition could ever be regarded as indubitable if it were first necessary to examine everything that may serve as evidence relevant to its truth-value. On the other hand, it seems that this impasse can be avoided only if it is possible to settle in advance the import of matters that have not been examined.

immediate experience

That it is in fact possible to settle the import of matters that have not been examined may be brought out as follows. The impossibility of checking all the consequences of an empirical proposition is often cited to support the view that empirical propositions must always remain dubitable. Nonetheless, many philosophers who employ this argument concede the indubitability of so-called "basic propositions," or a person's current reports of the immediate contents of his consciousness (for example, pains, sense data, thoughts). But however fragmented and ephemeral immediate experiences may be, they are not without innumerable conditions and consequences. Like those of empirical propositions (statements of fact about the world outside immediate consciousness), the truth-values of basic propositions are connected with those of an unlimited number of other propositions which may be construed as evidence relevant to them. Hence, if a person's current reports of the immediate data of his own consciousness are indubitable, it is not because he has surveyed everything that may serve as evidence relevant to them: rather, it is because his ground for making the report is such that he cannot reasonably acknowledge that any evidence could supersede it. Indeed, it is reasonable for him to require that all evidence be interpreted so as to be consistent with his report.

incorrigibility

When one proposition serves as evidence relevant to a second, it does so by virtue of certain other empirical or logical propositions (laws or rules) by which the two are connected. The connection may be broken or its nature altered, however, if the intermediary propositions upon which it depends are rejected or revised. Thus, the possibility of coming upon contrary evidence can be excluded by requiring that this alternative be adopted whenever necessary.

But under what conditions is it reasonable to make such a requirement of incorrigibility—to arrange that nothing count as evidence against a certain proposition? In some cases (for instance, when a mathematical proposition is supported by a well-understood proof, or when a basic proposition is grounded in immediate experience) it may seem fairly clear that the conditions are satisfied. However, philosophers have failed to provide a general account of these conditions; instead, they have usually limited themselves to identifying particular instances of their satisfaction. Some philosophers have claimed with considerable plausibility that certain elementary mathematical propositions (such as that 2 + 2 = 4) may be regarded as indubitable without proof, but they have done little to explain systematically why this should be so. With regard to empirical propositions, neglect of the problem of clarifying the conditions in which they may be accepted as indubitable has resulted in part from widespread controversy over whether the problem properly arises at all. That there are no such conditions is frequently maintained by philosophers (for example, Bertrand Russell, A. J. Ayer, C. S. Peirce, C. I. Lewis) who subscribe to certain popular epistemological doctrines—in particular, the doctrines that every empirical proposition is to be construed on the model of a scientific hypothesis, or that it is to be interpreted phenomenalistically as equivalent to an unlimited number of predictions.

Logical Contingency and Necessity

A more general obstacle to a sound understanding of the basis of indubitability lies in a tendency to look for it in the wrong place. A proposition is indubitable when there could be no reason to doubt it, but this impossibility is not in general inherent in the logical character of the proposition itself. Indubitability is an epistemic property that depends on the relation between a proposition and the evidence or ground for assent with which it is considered. In particular, dubitability and indubitability must not be confused with logical contingency and logical necessity. The logical contingency of a proposition does not as such entail that no one has conclusive evidence or ground for it, and a logically necessary proposition may reasonably be doubted by someone who is not in a position to appreciate its necessity and who therefore must concede the possibility that further inquiry will uncover evidence against it.

Moreover, it is a mistake to suppose that evidence for a proposition is not conclusive unless its conjunction with the denial of the proposition is self-contradictory. To be sure, a proposition is indubitable if and only if no basis for assenting to its alternative is conceivable, but something may be inconceivable even though it contradicts neither itself nor what has already been established.

Conditions of Rational Inquiry

The claim that a basis for doubt is inconceivable is justified whenever a denial of the claim would violate the conditions or presuppositions of rational inquiry. Avoidance of self-contradiction is perhaps the most familiar of these conditions, but it is not the only one. For instance, since inquiry is fundamentally an attempt to discriminate between what is to be accepted and what is to be rejected, nothing can rationally be conceived which involves denying the necessity for making these discriminations or undermining the possibility of making them.

A systematic explanation of dubitability and indubitability awaits, therefore, a general theory of the nature of rationality which illuminates the presuppositions and conditions that rationality requires. Furthermore, it awaits an account, developed from this theory, of the particular conditions in which propositions of various sorts must be regarded as indubitable if the possibility of rationality is to be preserved. Even if this were done, however, a further problem would remain. While an adequate theory of rationality would give a clear account of the conditions in which a proposition may reasonably be regarded as indubitable, it cannot of course guarantee that these conditions are correctly identified in any given case. To support the claim that a certain proposition is indubitable, it is not sufficient to understand the conditions in which such claims are justified; it is also necessary to know that the conditions are fulfilled in the particular case in question.

The Indubitability Regress

A disturbing pattern of argument seems to develop, however, in considering the proposition that a given proposition is indubitable. The proposition that the conditions for the indubitability of a certain proposition have been satisfied cannot itself be regarded as beyond doubt unless the conditions for its indubitability have been satisfied; but the satisfaction of these conditions is dubitable unless …, and so on.

But acknowledging this regress does not require one to concede that it is never reasonable to regard a proposition as indubitable. Rather, the view to which the regress leads appears to be that while there are occasions on which it is reasonable to regard a proposition as indubitable, it is never altogether indubitable just which occasions these are. There is an air of paradox here, perhaps, but there is no logical difficulty. The regress does not interfere with the possibility of there being satisfactory logical relations between indubitability claims and judgments establishing that these claims are reasonable. It only interferes with our confidence in ourselves, suggesting that there is always room for doubt as to whether we are being reasonable. Or, to put the matter a bit differently, the regress supports no more than the mordant comment that it is never reasonable to insist that the question of whether one is being reasonable is entirely closed.

Bibliography

In addition to loci classici in Descartes, Meditations on First Philosophy ; David Hume, An Enquiry concerning Human Understanding ; and Immanuel Kant, Critique of Pure Reason, there are particularly interesting and relevant discussions in the following more recent works: A. J. Ayer, The Problem of Knowledge (London: Macmillan, 1956); C. I. Lewis, An Analysis of Knowledge and Valuation (La Salle, IL: Open Court, 1946); N. Malcolm, "Knowledge and Belief," in Knowledge and Certainty (Englewood Cliffs, NJ: Prentice-Hall, 1963); G. E. Moore, "Four Forms of Scepticism," in Philosophical Papers (London: Allen and Unwin, 1959); and C. S. Peirce, Collected Papers (Cambridge, MA, 1935).

other recommended titles

Buryeat, M. F., ed. The Skeptical Tradition. Berkeley: University of California Press, 1983.

DeRose, Keith, and Ted Warfield, eds. Skepticism. New York: Oxford University Press, 1999.

Fogelin, R. Pyrrhonian Reflections on Knowledge and Justification. Princeton, NJ: Princeton University Press, 1995.

Greco, John. Putting Skeptics in their Place. New York: Cambridge University Press, 2000.

Hankinson, R. J. The Sceptics. London: Routledge, 1995.

Klein, Peter. Certainty: A Refutation of Scepticism. Minneapolis: University of Minnesota Press, 1981.

Lehrer, Keith. "Why not Scepticism?" Philosophical Forum 2 (1971): 283–298.

Roth, Michael, and Glenn Ross. Doubting: Contemporary Perspectives on Skepticism. Boston: Kluwer, 1992.

Sosa, Ernest. Knowledge in Perspective: Selected Essays in Epistemology. Cambridge, U.K.: Cambridge University Press, 1991.

Sosa, Ernest, and Enrique Villanueva, eds. Skepticism. Cambridge, MA: Blackwell, 2000.

Stroud, Barry. The Significance of Philosophical Skepticism. Oxford: Oxford University Press, 1984.

Williams, Michael. Unnatural Doubts: Epistemological Realism and the Basis of Scepticism. Oxford: Blackwell, 1992; corrected edition, Princeton, NJ: Princeton University Press, 1996.

Harry G. Frankfurt (1967)

Bibliography updated by Benjamin Fiedor (2005)

Encyclopedia of Philosophy