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تاريخ التسجيل : 26/10/2009
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 | |  Testimonial and juridical probability | |
Testimonial probability arises from the testimony of witnesses. It is one of the two kinds of probability which Silvester de Prierio listed in his Summa summarum (the other is endoxic probability): “‘Probable’ is used in two ways. First as the opposite of hidden, that is, what is proved by witnesses …”[23] The rapid growth of jurisprudence after the twelfth century nourished a great interest in witness testimony.[24] It was very difficult to rely on circumstantial evidence in medieval jurisprudence; so the testimony of witnesses was in many ways the key to a court decision. A complicated system of “half proofs” and proofs was designed to safe-guard the rationality of juridical procedures (Evans 2002; Franklin 2001, 15; Rosoni 1995, 89). Moreover, even outside the narrow confines of jurisprudence, witness testimony played an important role. Thomas Aquinas, for instance, described a certainty sufficient for action: - اقتباس :
- And yet the fact that in so many it is not possible to have certitude without fear of error is no reason why we should reject the certitude which can probably be had [quae probabiliter haberi potest] through two or three witnesses … (Thomas Aquinas, Summa theologiae, II-II, q. 70, 2, 1488)
Thomas’s remark alludes to the norm that the testimony of one eye-witness confers probability on an assertion, whereas the (uncontested) testimony of two or more witnesses creates probable certainty.A related but wider field for using the predicate “probable” in juridical terminology was the classification of presumptions. A “probable presumption” (probabilis presumptio) had some force in inclining a judge towards or against a verdict (Hubert 2009; Motzenbäcker 1958, 120, 159). Moreover, witness testimony was just one kind of evidence which could render a presumption probable. Probability could also result from “truth-like circumstantial evidence” (indicia verisimilia), as this statement from Huguccio documents: “Probable is what is accepted because of common human opinion or truth-like circumstantial evidence (indicia).”[25]Huguccio’s reference to common opinion shows that endoxic probability was also relevant in the law courts.[26] Nevertheless, the treatment of signs and indicia as probability generating evidence, which was strongly promoted by scholastic jurists, created an important precedent for connecting the notion of probability to the direct evidence of an observer. 3.4 Semantic probabilityAristotle tied the notion of probability to questions of necessity and contingency. The probable did not follow with necessity but only contingently (and for the most part) from the nature of things. In medieval scholasticism, this connection was often stated in semantic terms. Boethius of Dacia called probability: “a property which disposes (habilitans) but does not necessitate a subject to the partaking of a predicate”.[27] Probability is here a degree of participation of a predicate in a subject. Full participation under all conditions stands for necessity; participation under most conditions (for the most part) leads to probability. The semantic notion of probability as conditioned participation of a predicate in a subject is thus closely related to the proto-frequentist interpretation discussed above. It is, however, formally distinct as a notion of probability, not least because some scholastics addressed it as such. Peter Richeri, Topica Aristotelis (A. 37), I q. 2, 117ra-118ra, referred to Boethius (the ancient one, not the medieval philosopher of Dacia) in this context: - اقتباس :
- Yet Boethius defines probable things differently in his Topics I: probable things are those to which the mind readily acquiesces, although it does not possess a firmness of truth in them, as in this proposition: “If she is a mother, she loves [her child].” With respect to this explication, it should moreover be known that a proposition is called probable when its subject contains a property which disposes, but does not necessitate, it to partake of the predicate ….[28]
The semantic relation to which Richeri refers is not explicit in Boethius’s definition. What mainly matters here, however, is Richeri’s use of a semantic notion of probability. Albert of Cologne displays the same notion in connection with a perception-based explanation; such propositions are held true by everyone, the most, or the wise.[29] The less sense-based and the more intellectual a perception is the more is it restricted to the wise and the thoughtful, according to Albert. Interestingly, he acknowledges Arabic sources for this view (Albert Logica, I, 1, 2, 241; Bach 1881; Cortabarria Beita 1953). He does not mention a specific source, but this hint uncovers an important connection indicating that medieval Islamic philosophy, theology, and law were no less based on probability than their Christian counterparts (Black 1990, 108; Daiber 1990, 218; Miller 1984, 55).4. Further aspects of medieval probability 4.1 The dialectical syllogismSyllogisms are patterns of logical argumentation. A syllogism with merely probable premises was called dialectical in medieval and Renaissance philosophy. Since dialectic was the “art of rational disputation” or “controversial inquiry” (ars disserendi), and disputation was a characteristic activity of universities in the Middle Ages, argumentation with probable propositions possessed an enormous significance for medieval thought. It is also characteristic of logic-fed scholasticism that probable reasoning was mainly conceived as logical deduction from probable premises.[30] After the rise of Aristotelianism, these premises were mostly framed as endoxa. Thomas Aquinas writes: - اقتباس :
- The dialectician is concerned only with proceeding from propositions which are as acceptable as possible. These are propositions which seem true to most people and especially to the wise. (Thomas Aquinas, Posterior Analytics, I, 31, 3, 142)
It is not, however, clear whether authors who summarily refer to probable premises only intendendoxa in their definitions of dialectical syllogism, or whether they operate, like Albert of Cologne, with a broader notion of probable premise. Albert (Logica, I, 4, 2, 278) speaks with respect to the dialectical syllogism about premises which are always or most often (in pluribus) true. There was also some discussion about the epistemic status of the argumentative scheme of the dialectical syllogism and the conclusions from probable premises. The common assumption was that the dialectic syllogism is an indubitably valid deductive scheme, but that probable premises produce only probable conclusions or opinions (Buridan, Quaestiones, 19; Buridan,Summulae, 347).However important dialectical syllogisms may have been for medieval disputation, it should also be recognized that action-planning in conscience was conceived as deduction from (partly) probable premises. The dialectical syllogism therefore provided a logical basis for moral decisions and served as a tool for moral theology.The humanist dialectic of the Renaissance shared many assumptions concerning the dialectical syllogism with the scholastics, but some authors developed a different understanding of dialectic. These developments will be discussed in Section 5. 4.2 Order relations between probabilitiesPre-modern probability was not a number or ratio, but mainly a binary property which a proposition either had or did not have. Yet pre-modern probability was also an ordinal concept. Some propositions were regarded as more probable (probabilior, probabilius) than others. More probable opinions were a subclass of probable opinions. Consequently, an opinion had at least to be probable in order to be more probable than another opinion. In line with these premises, strict order relations (i.e. “>” and “<”) for opinions were common in medieval and Renaissance philosophy. Interestingly, ascriptions of equal probability seem to be rare before the sixteenth century. An equal balance of reasons gave rise to doubt (dubium). The moral rules for decisions in doubt, however, were different from those for the choice between probable opinions. Hence, doubt should not straightforwardly be equated with equal probability, in particular in medieval scholasticism. Further research is needed to uncover the role of equi-probability in the period 1200–1500; until then, we can only be sure that in this period the possibility of a strict ordering was envisaged for probabilities. 4.3 Both-sided probabilityScholastic authors often ascribed probability at the same time to a proposition and its negation or to a proposition and a counter-proposition which was logically incompatible with it. A proposition could even be regarded as more probable (probabilior) without its negation losing probability. In fact, calling an opinion more probable than another regularly implied that the other was also probable, because comparison and choice between probable alternatives was intended.For some modern commentators, this impugns an understanding of “probable” as readily affirmable or adoptable. It seems to be a minimum requirement of being affirmable that a proposition x is judged to be more likely true than false, that is, having probability p (x) > 0.5. Since a proposition and its negation cannot both have p > 0.5, they cannot both be affirmable at the same time. The scholastics, of course, did not operate with such numerical considerations. For them, “both-sided probability” (as I have termed it) resulted naturally from the endoxic concept of probability. A proposition and its negation can both be held true at the same time by different experts.[31] There are two different ways in which an evaluator can consider a proposition as more probable and a counter-proposition as probable at the same time. First, the evaluator can believe that more and/or better experts hold x true than y, although y is approved by a sufficient number of experts to count as probable.[32] Second, the evaluator may consider a proposition as more probable according to her own weighing up of the reasons, while the counter-proposition is considered probable because it is the opinion of many or weighty experts.[33] Both options show that there is no obvious logical problem with the assumption that two incompatible propositions can both be regarded as rationally affirmable.[34] This does not, however, invalidate the claim that only one of the propositions can be rationally affirmed at a given time and by a given person from her own standpoint. The person in question can, it seems, only rationally affirm what she regards as more probable than its negation. Consequently, regarding a rival opinion as probable means considering it as affirmable by others – or, in modern terminology, by one’s epistemic peers.[35] This insight is an important step towards opinion pluralism, and it is significant that it is in nuce implied in the both-sided probability of medieval scholastics.The epistemological difficulties of both-sided probability were not, however, analyzed in depth by medieval scholastics. Nor did they investigate how an epistemology of acceptance of probable opinions as premises for action differs from one which assumes assent or affirmation of the opinions in question. All this happened much later in the scholastic tradition, in the seventeenth century; but this is another story (Deman 1936; Fleming 2006; Gay 2012; Knebel 2000; Schüssler 2003). 4.4 Subjectivity and objectivityThe question of whether medieval forms of probability were subjective or objective has long puzzled modern researchers (Kantola 1994). It is difficult to come up with an answer, not least because medieval authors did not employ the (characteristically modern) terminology of subjectivity and objectivity with respect to judgments of probability. Nevertheless, the discussion above of medieval uses of probability-related terms sheds some light on matters of subjectivity and objectivity.As has been shown, probabilis or verisimilis were predicates for the qualitative support a body of evidence gave to the truth of a proposition or the fittingness of a sign. We have already seen what kinds of evidence for probability were accepted at the time. A subjective aspect of probability ascriptions thus consisted in a belief obtained by the supporting relationship in a particular case. An objective aspect depended on the actual existence of the supporting basis.This kind of objectivity does not make probability a feature of the world or a theoretical construct based on facts of nature. Such stronger forms of objectivity underlie, for instance, a true proto-frequentist understanding of probability.[36] If probability means “what frequently happens”, probability will often derive from objective features of the world. If frequent occurrence of x is only an indicator for the affirmability of sentences about x, medieval proto-frequentist probability is not strongly objective in this way. Nevertheless, at least the medieval semantic notion of probability seems to be objective in the strong sense. A proposition, the predicate of which mostly inheres in its subject, is at least in some cases objectively probable on ontological grounds from a scholastic point of view. Facts of nature determine the degree to which predicates inhere in a subject, so that it becomes objectively probable that a mother loves her child.Moreover, medieval probability ascriptions were in significant respects inter-subjectively testable – and it is characteristic of scholasticism to assume that communities are in a position to assess individual claims of rationality.[37] Propositions can be identified as semantically probable through the common use of terms. A communitarian basis also existed for the endoxic notion of probability, which in principle derives from observable majorities or a shared ascription of wisdom or expertise. Endoxic probability could thus become an instrument of social (and moral) control. Yet, although collective control of endoxic probability ascriptions may have existed, it was never absolute in the period under discussion. Often, no consensus concerning the relative weight of experts existed; and it therefore remained contentious which side was “larger and more reasonable” (maior et sanior) or even whether a proposition was supported by enough leading experts to count as probable. On these grounds, some perspectival variation became possible. Walter Burley wrote that a thing can be probable to one person and improbable to another.[38] This statement shows that a limited multi-perspectival variety of probability ascriptions was acknowledged in the late Middle Ages. | |
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