To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
A crucial methodological recourse in matters of deliberation and inquiry, common sense has a dual bearing. On the positive side, there is a strong pro-presumption that any answers we give to questions of policy and procedure shall incorporate and stand in confirmation with our common-sense beliefs on the matter. On the negative side, there is a strong con-presumption against any rejection or abandonment of common-sense beliefs, and a cogent justification should be provided for any step in this direction. Methodologically, the common-sense approach exerts a strong constraint on our procedures of explanation and validation. This chapter explores how we should think of methodology in common-sense philosophy. Common sense is neither a cognitive faculty nor a way of producing beliefs. A common-sense belief is not produced in a certain way but rather a particular sort of belief, that is, one that is available to people in general on account of its triteness, its palpable obviousness. A common-sense belief is pervasive among the members of a community on the basis of their shared experiences in managing everyday affairs. Common-sense beliefs address matters of everyday run-of-the-mill; they relate to what transpires within the sphere of the ordinary course of things in everyday life.
The aim of this essay is to set out an argument for moral objectivity. A brief sketch of the considerations at issue should help make it possible to keep sight of the forest amid the profusion of trees.
Without some recourse to presumption we simply could not manage to obtain the informative inputs indispensable for answering our questions about factual issues. Some degree of presumption (however small) incredibly attaches to our procedurally validated truths throughout the factual area where defeasibility is virtually inescapable. This becomes clear once one considers the issue of the observational inputs essential to inquiry in the factual domain. If their status always had to be that of established truths, we could never get off the ground, since observational experience just does not work like that. Thus if an “ordinary process of inferential reasoning” were at issue here, we would be in deep trouble as any such process can only extract truths from truths, and if the inputs themselves had to be established truths, the whole process would be vitiated at the outset. Happily this is not so. An inquiry procedure is clearly not an “ordinary process of inference”: it must afford an originative mechanism, capable of yielding an output of (putative) truths without demanding an initial input of previously established (putative) truths. Clearly if we hewed to the line that rationally discursive procedures can only extract truths from truths, we would be offered the unattractive choice between (1) accepting a “starter set” of nondiscursively self-evident or self-validating truths, or (2) a skepticism that admits defeat and gives up the whole project of a rational validation of truth-acceptance. This dilemma can be addressed effectively by resorting to presumptions.
Theorists of knowledge have long recognized and emphasized that there are significant differences between theoretical and practical reason, between problem solving in purely theoretical matters (where nothing is at stake save the possibility of mistaken beliefs), and in practical matters (where actual harm of some sort might be incurred). There is, perhaps, no more striking illustration of this situation than the little heeded issue of the treatment of very remote possibilities – those whose probability is extremely small. Here the question before us is this: in regard to matters of practice, should a diminutive probability (one of an effectively infinitesimal magnitude ∈) be seen as being indistinguishable from zero and treated as having no magnitude at all? In deploying probabilities in expected-value comparisons that serve as guides for decision making, could and should we adopt theequation: ∈ = 0? Are we to dismiss those minute probabilities and presume them to be zero? Sometimes the answer is a decided affirmative. And this chapter accordingly addresses one very special case of presumption that answers in relation to our planning for the future, namely, the dismissal of diminutively far-fetched possibilities from our reckoning.
Effectively Zero Probabilities
Probability and cognitive presumption are closely interconnected. The step from probability to presumption is mediated by the consideration that when answers are needed the probability of the available alternatives can help to provide guidance.
Most philosophical theorists of knowledge – the classical rationalists (like Descartes and Spinoza) and empiricists (like Hume) as well as various later thinkers from Brentano to our contemporaries – have been concerned primarily with knowledge in the sense of what we know for certain. In consequence it has transpired that – apart from forays by mathematically oriented theorists such as F. P. Ramsey, J. M. Keynes, and R. Carnap into the domain of probability – contemporary epistemology has almost wholly neglected the range of conceptions in the region of uncertainty, the gray area of concepts that, like presumption and plausibility, have an indecisively tentative impetus toward truth.
The quest for certainty has continued to exercise a virtually hypnotic fascination on contemporary theorists of knowledge, who have, accordingly, tended to neglect cognitive claims that stop short of pretentions to definitive finality. But by rights epistemology should surely be seen as having a far broader range, concerned not just with knowledge as such but with a great variety of cognitive matters such as belief, conjecture, supposition, and much else. And it is just here – in the theory of cognition at large – that the concept of presumption comes into its own and provides a healthy antidote to the fundamentalist epistemologies whose inadequacy to provide an adequate theoretical basis for rational inquiry has become increasingly evident in recent years.
The topic of default reasoning also affords instructive insights into the nature of presumptions. A default in logic is a fall-back position in point of conclusion-drawing – one to which we can appropriately resort when circumstances prove uncooperative. But of course things ought not to go wrong in logic. So what is going on here?
Orthodox inferential reasoning proceeds via logically valid inference processes which do – and must – proceed from true premises to true conclusions. They review the inherent connections coming actually or assumptively accepted commitments. Logic functions within the limits of the given. By contrast, default reasoning – which involves an information gap between premises and conclusion – goes beyond this into uncharted territories. In consequence, plausible (though sometimes false) premises will lead to plausible (though possibly false) conclusions.
The logical validity of inference rules in standard (truth-functional) logic is determined on an input-output basis, a valid rule being one that will invariably yield true outputs (conclusions) from true inputs (premises). All such inference rules will faithfully and unfailingly transmit the truth of premises to the conclusions. By contrast, the inference processes of default logic are such that the truth – real or suppositional – of the premises does not assure the truth of the conclusion but will at most establish that conclusion as contextually plausible. Such inferences are ampliative: the conclusion can go beyond what the premises guarantee.
Philosophers of science often puzzle about the prominent but yet problematic role of such theoretical factors of inductive reasoning as regularity, continuity, simplicity, uniformity, conservation, and the like. It would clearly be problematic to regard such factors as representing fundamentally ontological facts about the world – an inclination on the part of nature itself (to put it somewhat anthropomorphically). It would, however, make perfectly good sense to view such factors as representing principles of procedural presumption – forming part of the regulative or methodological mechanism of our vehicles of explanation. One thereby avoids treating such features of systematicity as substantive findings about nature but rather as methodological, and procedural guideposts for our conduct of scientific inquiry – procedural principles of plausibility that constitute our evaluative standards for explanatory accounts.
In this way, a positive presumption of acceptability is taken to operate in favor of all the traditional parameters of systematization: consistency, uniformity, regularity (causality, rulishness, and lawfulness in all forms), simplicity, connectedness/coherence, unity/completeness, and the rest. These various defining facets of systematicity thus come to do double duty as elements of a criteriology for acceptability-as-true and as presumptive principles regulatively governing the conduct of inquiry. The resulting situation is set out in Display 9.1.
To presume in the presently relevant sense of the term is to accept something in the absence of the further relevant information that would ordinarily be deemed necessary to establish it. The term derives from the Latin praesumere: to take before or to take for granted.Presumption has figured in legal reasoning since classical antiquity. There is nothing modern or cutting-edge about it: it is one of the oldest tricks in the book.
Presumption found its first and still most prominent role in the context of the law, where a presumption mandates a trier to accept a certain fact once some other correlative fact has been established. The French Code civil defines “presumptions” as “Consequences drawn by the law or the magistrate from a known to an unknown fact.”Legal presumptions provide a way of filling in – at least pro tem – the gaps that obtain in conditions of incomplete information. (The “presumption of innocence” provides a paradigm example here.)
Such a legal presumption (praesumptio juris) is an inference from a fact that, by legal prescription, stands until refuted. Presumption of this sort is a gap-filling resource: it comes into operation only in the absence of relevant information or evidence, and it leaves the scene once suitably strong evidential indications come to view. One authority has elucidated the conception of presumption in the following terms:
A presumption in the ordinary sense is an inference. … The subject of presumptions, so far as they are mere inferences or arguments, belongs, not to the law of evidence, or to law at all, but to rules of reasoning.[…]
Whenever we act and actually do something on the basis of a presumption we take a step beyond it: we make the assumption that it is correct. This assumption may turn out to be incorrect. But even if so, this nevertheless does nothing to unravel the validity of that initial presumption in the circumstances under which it arose. Its erroneousness is a matter of hindsight unavailable before the fact and represents a misfortune rather than a mistake.
The appropriateness of presumptions is not to be assessed on an individualized retail basis; instead the matter is one of wholesale – of the statistically systemic appraisal of the principles of presumption that underlie the particular case. Presumption is a methodological and procedural resource and must be judged on that basis through its performance “on the whole.” Thus epistemic presumptions exist to enhance our access to usable information, and communicative presumptions exist to facilitate the transmission thereof. The ultimate test of the appropriateness and validity of our presumptive proceedings in their various domains will be a matter of their efficacy in the realization of the correlative purposes – an ultimately pragmatic standard.
In the late nineteenth century, C. S. Peirce in the United States and Ernest Mach in Europe suggested an evolutionary rationale for certain presumptions such as trust in the senses and in various analogies.
“Dr. Livingston, I presume” runs the famous exclamation with which H. M. Stanley greeted the long-lost explorer. And in saying this he as much as said that “this is what I am going to take to be the case unless and until further developments should show that it is not.” That is just exactly how presumption works.
The topic of presumption encompasses a wide range of practices within our quest for informative knowledge and practical decision. These particular resolutions, however, have a tentative quality in being taken to hold not with categorical assurance but rather provisionally and pro tem until such a point when (if ever) sufficiently strong counterindications come to light. Such presumptions carry a burden of proof that inclines upon anyone who is disinclined to accept them.
The practice of presumption arose initially in the law but subsequently became operative in virtually every area of rational endeavor, for presumption is a remarkably versatile and pervasively useful resource. Firmly grounded in the law of evidence from its origins in classical antiquity, it made its way in the days of medieval scholasticism into the theory and practice of disputation and debate. And it subsequently extended its reach to play an increasingly significant role in the philosophical theory of knowledge. It has thus come to represent a region where lawyers, debaters, and philosophers can all find some common ground.
Presumption is closely bound to the idea of burden of proof (onus probandi), which is also at root a legal conception. It functions in the context of an adversarial proceeding in which one party is endeavoring to establish and another to rebut some charge before a neutral adjudicative tribunal. The very phrase (onus probandi) derives from classical Roman law where it affords one of the ground rules of probative procedure, governing the division of the labor of argumentation between plaintiff and defendant, which specifies tasks of marshaling evidence. Under the Roman system, nothing was conceded in legal actions as admitted: the plaintiff, as the initiating agent in laying a charge, had to make his case first (agenti incumbit probatio), then the defendant's countercase was argued on his exceptio, and thereafter the plaintiff's on his replication, and so on. The burden rested with the plaintiff in civil cases and with the state (as surrogate plaintiff) in criminal cases. Throughout, the “burden of proof” lay with the side active in making the allegations, subject to the fundamental rule that “the need for proof lies with him who affirms, not him who denies.”
The idea of burden of proof embodies a basic ground rule of the probative process. To say that the burden of proof rests with a certain side is to say that side must adduce the substantiation required to make its case.
Presumptions obtain principally with two ends in view. On the one hand there are the purely cognitive presumptions made for the sake of answering our questions and filling gaps in our information (as, for example, presumptions regarding the reliability of sources). On the other hand there are practical presumptions made for the sake of guiding our decisions regarding actions (as with legal presumptions that facilitate the resolution of cases; for example, that someone long missing is dead so that the person's estate can be distributed). At present, however, the cognitive sector of presumption will be at the focus of concern, with presumption as a source of (putative) information about the truth of things in the forefront.
A cognitive presumption stakes a claim that outruns the substance of actually available information; it is a proposition that, in suitably favorable circumstances, is accepted as true in the absence of any counterindications. This is a default position affording an answer to some question of ours that we adopt for lack of anything better and will keep in place until such time as something comes along to eject it from this position of favor. In this way, cognitive presumptions function as instrumentalities of rational economy. Thanks to them we need not remain bereft of answers to our questions until all the relevant returns are in – which is to say virtually never.
Presumption is a remarkably versatile and pervasively useful resource. Firmly grounded in the law of evidence from its origins in classical antiquity, it made its way in the days of medieval scholasticism into the theory and practice of disputation and debate. Subsequently, it extended its reach to play an increasingly significant role in the philosophical theory of knowledge. It has thus come to represent a region where lawyers, debaters, and philosophers can all find some common around. In Presumption and the Practices of Tentative Cognition, Nicholas Rescher endeavors to show that the process of presumption plays a role of virtually indispensable utility in matters of rational inquiry and communication. The origins of presumption may lie in law, but its importance is reinforced by its service to the theory of information management and philosophy.