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تاريخ التسجيل : 26/10/2009
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 | |  Medieval probability-related terminology | |
Terms, such as the Latin probabilis were already in use in the early Middle Ages and can, for instance, be found in Carolingian texts on rhetoric (e.g., Alcuin, Rhetoric, 113). The ancient authorities on the subject were Cicero and Boethius, whereas Aristotle’s most seminal statements on probability-related concepts became known only after the middle of the twelfth century (see Cox and Ward 2006; Fredborg 1988, 150; Greenberg-Pedersen 1984). Particularly significant in this respect were the introduction of Aristotle’s Topics into academic discourse in the middle of the twelfth century (but the full impact was not felt before 1200) and the new translations of Aristotle’s Nicomachean Ethics and Rhetoric in the thirteenth century.[3] By the end of this century, Aristotle’s definitions had largely (though not entirely) supplanted those of Cicero and Boethius in scholastic thought. The impact of this change should not be exaggerated because the notions of probability held by Cicero and, in particular, Boethius were in significant respects close to those of Aristotle.The main probability-related terms in this period were probabilis, verisimilis, credibilis,opinabilis, and some expressions indicating frequency such as ut frequenter, ut in pluribus, andfrequentius. We need to look carefully at the specific meanings of these words and phrases before proceeding to concepts of probability in a narrower sense. 2.1 ProbabilisProbabilis was the most important probability-related predicate in the Middle Ages (and in the whole scholastic tradition). It is often possible to translate probabilis as ‘probable’ in an ordinary language sense, but attention should be paid to meanings arising from a combination with particular nouns. The predicate probabilis mainly pertained to propositions, sentences, or opinions, but these are not the only meaningful referents. Sometimes persons were described as probable, as in the phrase “the more probable philosophers” (philosophi probabiliores). Thomas Deman (1933, 262) renders this phrase as “the philosophers who deserve most consideration”; but one could also translate it as “the philosophers who are more likely to find the truth”. Signs were also sometimes called probable (signum probabile), as in Silvester de Prierio’s Summaunder the heading ‘probabile’. Last but not least, probability was attributed to events, for instance, when Thomas Aquinas, in Summa theologiae II-II, q. 32, 5, 1322, says “according as things probably and generally occur / according to what probably and generally occurs” (secundum ea quae probabiliter et in pluribus occurrunt). As we shall see, however, it is conceivable that all these assertions are elliptic references to the probability of propositions.A proposition was probable (probabilis) if specific indicators of truth justified assent (i.e., holding it true) or acceptance as a premise for action.[4] The main justifications for judgments of probability will be discussed in more detail in Section 3, on “Scholastic Concepts of Probability”. For the moment, it is enough to say that authority, testimony, a sufficient (but not maximal) appearance of truth, and frequent truth could buttress an ascription of probability.The most prolific category of probable propositions were opinions in the medieval technical sense of this term. An opinion (opinio) was often defined as a proposition held to be true but which the person holding it feared might be wrong (see Byrne 1968, Franklin 2001). The fear in question results at least in part from an awareness that one’s judgment might be fallible. The category of opinion stood below faith or full conviction (fides) and knowledge (scientia) in a widely shared medieval ranking of epistemological confidence and doxological firmness.[5] All three epistemic attitudes involved assent, but only faith and knowledge implied full subjective certainty (certitudo).On this basis, “probable opinion” (opinio probabilis) became a standard term for a class of propositions held to be true, which humans had to be content with in many fields of investigation. In these fields, human fallibility or the changeable nature of the subject matter precluded full knowledge (scientia), and a lack of religious relevance or accepted theological contentiousness prevented the intervention of faith (fides). The scope of this domain was enormous. In philosophical theory, it was the home-ground for dialectical argumentation and dialectical syllogisms (see Section 4.1); on a practical level, it was regulated by counselors of conscience and lawyers.For the regulation of consciences, another standard term was ‘probable certainty’ (certitudo probabilis). Probable certainty forestalled sin by enabling one to base one’s actions on correct probable reasoning. Since reasoning which went beyond the probable was virtually unattainable in many moral contexts, an agent satisfied her or his epistemic duties by relying on sound probable reasoning, thus acquiring a subjective certainty of having done all that could be expected of an agent to avoid sin (Gardeil 1911; Schüssler 2003, 50). In the opinion of many medieval scholastics, probable reasoning could not generate epistemological certainty; the phrase “probable certainty”, however, sprang from compliance with moral demands (which we would call epistemic duties today) and not from strong conviction based on evidence. Perhaps because of the risk of misunderstanding it implied, ‘probable certainty’ was largely supplanted, from the fifteenth century onward, by the similar concept of ‘moral certainty’ (certitudo moralis), (Franklin 2001, 69; Knebel 2000, 55; Schüssler 2009).In the field of jurisprudence, the term probabilis was typically combined with presumptions (presumptiones). A probable presumption for or against a culprit was one that in itself did not suffice to incline a reasonable judge to a verdict (only vehement or violent presumptions could achieve that). Nevertheless, probable presumptions had some juridical weight (in contrast to careless presumptions, presumptiones temerariae) and could be aggregated to justify a verdict (Franklin 2001, 43). 2.2 VerisimilisIn medieval usage, verisimilis meant what it literally said: that something was ‘truth-like’. This did not, however, imply that the thing was actually close to truth, because it might have only the appearance – possibly spurious or superficial – of truth. Signs, images, and circumstantial evidence were often called verisimilis if they satisfied these conditions. Medieval lawyers spoke of ‘truth-like circumstantial evidence’ (indicia verisimilia), and Albert of Cologne (Logica, 241) maintained that what was ‘truth-like’ resided in ‘signs’ (verisimile est in signis).[6]Was verisimilis used as a synonym for probabilis by medieval scholastics? Albert (ibid.) claims straightforwardly that “probable things are truth-like” (probabilia … sunt verisimilia).[7] Other scholastic uses of these words suggest instead a mere relation of frequent mutual implication. Probable opinions were usually truth-like because their probability prima facie justified an assumption of truth. Truth-like signs often justified an ascription of probability to an assertion. The widespread combination of probabilis with particular kinds of proposition (Aristotelianendoxa; see Section 3.1) and of verisimilis with signs are nevertheless good reasons to assume that these predicates were not synonymous. The distinction between the terms may reflect established differences in ancient Greek terminology, tying probabilis to pithanon (persuasive, adoptable) and verisimilis to eikos (truth-like). Such differences arguably already pervaded Cicero’s usage of probabilis and verisimilis, although the matter is contentious.[8] 2.3 Credibilis, opinabilisA proposition was regarded as credibilis or opinabilis if it could legitimately be accepted as one’s opinion. The underlying criteria were often the same as for probabilis. Propositions which did not satisfy the respective criteria were called inopinabilis or improbabilis, and deserved to be rejected by rational and responsible epistemic agents. This meant that improbable propositions ought not to be taken for true or accepted as a premise for action, but not necessarily that they must be regarded as false.[9] 2.4 Frequency termsA host of frequency terms such as “frequently” (frequenter), “more frequently” (ut frequentius) and “for the most part” (ut in pluribus), or their converses such as “rarely” (ut in paucioribus), often accompanied ascriptions of probability in medieval scholasticism. What frequently or usually happened was prima facie considered to be probable. Scholastic usage of frequency terms followed ancient precedent, most notably Aristotle’s statements of what is true or false “in most cases” (hōs epi to polu). Whether this background in Aristotelian science and methodology justifies the assumption of a medieval frequency concept of probability will be discussed in Section 3.2.3. Scholastic Concepts of ProbabilityIn some areas of medieval thought, probability-related terms were important for the regulation of decision-making and conduct. In these contexts, the term “probable” (probabilis) took on a specific significance. Whether a merchant wanted to follow an opinion concerning the moral legitimacy of a contract or a lawyer formulated a presumption, it had to be probabilis to possess moral or juridical weight. It is now necessary to discuss the most important medieval understandings of probabilis, grounding them in ancient definitions or precedent.Until the thirteenth century, the definitions of “probable” by Cicero and Boethius very much shaped the medieval understanding of probability: - اقتباس :
- That is probable which for the most part usually comes to pass, or which is a part of the ordinary beliefs of mankind, or which contains in itself some resemblance to these qualities, whether such resemblance be true or false. (Cicero, De inventione, I.29.46)
Something is readily believable (probabilis) if it seems true to everyone or to the most people or to the wise – and of the wise, either to all of them or most of them or to the most famous and distinguished – or to an expert in his own field, for example, to a doctor in the field of medicine or to a pilot in the navigation of ships, or, finally, if it seems true to the person with whom one is having the conversation or who is judging it. (Boethius, De topicis, 1180b28) For Cicero, probability represents the usual course of events, commonly held beliefs, or what resembles them. His characterization of probability thus contains the roots of at least two different concepts of probability. Boethius repeats Aristotle’s definition of an endoxon (see Section 3.1) as a readily believable proposition almost verbatim and calls it probabilis. In this respect, he prepared the way for the reception of Aristotle’s original definition; but note that Boethius addresses the role of experts more explicitly than Aristotle, who in medieval translations summarily refers to sapientes, the wise.[10]Aristotle replaced Cicero and Boethius as supreme authority on probability in the thirteenth century. This is also the time when medieval probability discourse fully unfolded. For the period from (roughly) 1200 to 1500, it is possible to identify four different concepts of probability: the endoxic, proto-frequentist, testimonial or juridical, and semantic. The number of concepts is, however, a matter of interpretation since it is possible to split up the juridical category of probability further.[11]The use of probability-related terms was almost certainly wider than the concepts of probability listed above suggest. In philosophical and theological debates, as well as in the regulation of action, probabilis could be used as a predicate for the argumentative support which a proposition had (translatable as “plausible” or “rationally tenable”). In the early modern era, this aspect of medieval probability became explicitly integrated into the definition of a probable opinion (Knebel 2000; Maryks 2008; Schüssler 2006). It was not, however, expressly addressed in medieval and, in particular, scholastic characterizations of probability. Here, the focus will be on such characterizations in medieval sources. | |
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