Fuzzy Logic and Judicial Decision-Making: A new Perspective on the Alleged Norm-Irrationalism

Autore:Tecla Mazzarese
Carica:Instituto giuridico, Strada Nuova, 65, 27100 PAVIA (Italy)

    I wish to thank E, Bulygin, P. Comanducci, A.G. Conte, G. De Nova, R. Guastini and M. Taruffo for their stimulating comments and remarks on a first draft of this paper. I already presented some of the theses which occur in it in: Fuzzy Logic and Judicial Decision-Making: The Peril of a Rationalist Fallacy. This research has been carried out with the financial support of the Italian Ministero dell'Universita e della Riceica Scientifica e Tecnologica.

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@0. Introduction

According to a long-lasting and widespread view, judicial decision-making as a matter of fact can be, and as a matter of principle should be, logical-deductive In nature, I.e. judicial decisions can and should be taken following the classical logical rules of Inference. Thus, It Is rather common to characterize a judicial decision as a syllogism - or, along the more recent and refined analyses, as a chain of syllogisms - which Is termed "judicial" not because of some peculiar logical feature, but simply because It Is drawn within the scope of judicial activity. Notwithstanding the variety of shortcomings and unsatisfactory features which several scholars have denounced of such a view, the theory of judicial syllogism enjoys a large acceptance since, despite of all criticism, It Is still conceived as the main guarantee for the rationality of decision-making, and hence as a necessary means to securing that the highly purported value of legal certainty can be attained,

Thus, no surprise that whoever dares to point out problems met by the logical-deductive theory of judicial decisions Is Immediately blamed as an Irrationallst and condemned as a supporter of decisionism and arbitrary subjectivism of judiciary. It Is not by chance - just to mention a well-known example - that H. Kelsen's later standpoint on law and logic has been labelled as an expression of norm-irrationalism1. It Is not by chancePage 14 that the debate to which Kelsen's standpoint has given a start is focused on the opposition between norm-rationalism and norm-irrationalism.

On this background, the twofold contention of this paper is to argue that insofar as judicial decision-making is concerned (a) the opposition between norm-rationalism and nomr-irrationalism is misleading since is grounded on arguments which are ideological rather than theoretical in nature, and (b) that fuzzy, logic might acquire a relevant role in showing a way out from this sterile and deceptive opposition.

Given these two aims, my paper is diYided into three main parts. In the first part (ß 1.) I will mention three main sources of problems met by the logical-deductive theory of judicial decisions, and I will refer to the logical-theoretical apparatus of fuzzy calculi as a potential means to deal with, and to account for, such problems. Then, in the second part (ß 2.) I will distinguish two opposite theses concerning the putative explanatory power that the logical-theoretical apparatus of fuzzy calculi can be maintained to have insofar as a suitable account of prominent features of judicial decision-making is concerned. Finally, in the third part (ß 3.) I will concentrate on the sense according to which fuzzy logic can be taken to provide an appropriate theoretical ground which enables us to find a way out from the misleading opposition between norm-rationalism and norm-irrationalism.

@1. Fuzzines and judicial decision-making

Fuzzy logic has not yet acquired a prominent role in legal theory investigations and in particular it is far from enjoying a widespread attention in judicial decision-making inquiries. Thus, in this part of my paper, firstly (ß 1.1.) 1 will put forward some preliminary remarks which might explain the reason why the formal treatment of fuzziness has been so largely ignored by legal scholars. This undertaking obviously does not amount to either a justification, of, or a consent with, such an attitude. Rather, it is meant to be an attempt to point out some assumptions on which the misleading opposition between norm-rationalism and norm-irrationalism relies.

Then (ß 1.2.), turning to a closer inspection to the role which fuzzy logic may acquire in dealing with judicial decision-making, I will mention three main sorts of criticism addressed to the logical-deductive theory of judicial decisions and I will concentrate on the potential role of fuzzy logic in analysing judicial decision-making both because of the fuzziness of judicial language (ß 1.2.1.) and because of the fuzziness (or more correctly: the approximate nature) of judicial reasoning (1.2.2.).

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@@1.1. Fuzzy Logic: A Neglected Conceptual Apparatus

As far as I know very few legal scholars have paid attention to the import of the recently developed and everyday increasingly developing formal-logical treatment of fuzziness on several issues they work on.

It might be the case that the lack of interest is just apparent, that is not the result of an intended reaction, but a phenomenon simply contingent in nature; fuzzy logic and fuzzy set theory are newborn fields of research dealt with by a relatively confined number of adepts using highly sophisticated logical and mathematical tools2. Though sound, this hypothesis is not completely convincing. To be sure, in the Fifties and Sixties the newborn modern deontic logic gave rise to immediate and very confident (at times perhaps even too confident) expectations with regard to its potential heuristic power for traditional as well as for pioneering legal investigations.

Thus, it might very probably be the case that the lack of interest in the formal treatment of fuzziness is real, that is the result of an intended reaction stemming from a steady view, theoretical in nature: according to a deeply rooted opinion, legal scholars neither make any effort to elaborate, nor are fascinated by, conceptual tools enabling them to stress and to take in due account fuzziness. Rather, they look for means allowing them to get rid of it and when such an enterprise cannot be completely successful, they do their best to confining and regimenting whatever - in any legal context - is fuzzy or might convey some sort of fuzziness.

Two arguments supporting this second hypothesis are provided by (i) a plausible explanation the hypothesis at issue can suggest with regard to the radical different reactions to deontic calculi and to fuzzy calculi, respectively, and (ii) the prevailing attitude among logicians towards the formal treatment of fuzziness.

(i) Fuzzy calculi - contrary to what is the case with most deontic calculi - are not an extension of classical logic, they belong to what are usuallyPage 16 termed "deviant logics"3, that Is to say to those logics in which some of the fundamental laws of classical logic fail to hold (i.e.: are not valid). In view of this fact legal scholars divergent responses to these two new branches of modem formal logic can be given a very simple explanation.

Insofar as deontic logic is concerned, several legal scholars have been feeling confident to It from the very beginning of its first developments because most of Its calculi - being an extension of classical logic - preserve the standards of rationality at which legal theory aims to attaining. Under this respect It Is Interesting to recall the way G.H. von Wright describes Kelsen's reaction to his first contact with deontic logic In 19524:

[Kelsen] was very excited about the prospects which deontic logic seemed to open for vindicating some basic tenets In his own "pure" theory of law. In particular, he looked for support in logic for his idea that a legal order Is of necessity closed, i.e. that there are no "gaps" in the law, and for the Idea that a legal order must be free from 'contradictions'5.

Insofar as fuzzy logic is concerned, several legal scholars might be feeling reluctant rather than confident to It since - being fuzzy logic a deviant logic - It Is doubtful what sort of rationality (if any) its calculi can convey. Further, because of its specific concern fuzzy logic leads to ascribe Importance to what legal scholars would rather try to get free from In any legal context.

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(ii) in logic - similarly to what happens in legal theory - fuzziness is mainly conceived as a source of troubles and difficulties. Thus, as a matter of fact there is a sort of scepticism towards the attempts of its formalization. The arguments on which such a scepticism is based do not significantly differ from the reasons put forward for the elimination of fuzziness from legal contexts.

Though it is acknowledged that fuzziness is a peculiar feature of natural languages, still several outstanding logicians feel uneasy to take it into account in their formal calculi, That is mainly so, since quoting S. Haack:

an important reason for constructing formal systems of logic is to supply precise canons of validity - a major advantage of formal logic over unregimented informal argument is its much greater rigour and exactness. In view of this point it is not surprising that Frege and Russell should have regarded vagueness as a defect of natural languages, to be banished from an acceptable formal language. [...] This perhaps suggests that it would be appropriate simply to exclude vague sentences as ineligible for logical treatment6.

@@1.2. The potential Role of Fuzzy Logic in Analysing Judicial Decision-Making

The traditional logical-deductive theory of judicial decisions leaves no room for fuzziness: it is simply ignored if not downright denied that fuzziness can be a feature of decision-making both with regard to its constitutive elements and with regard to the patterns of reasoning which lead the decision-maker to take a judicial decision. Thus, a judicial decision is conceived as a logical inference drawn along the syllogistic schema: the norm of the case (i.e. the norm expressed by the conclusion of a judicial decision) being viewed as the logical conclusion of a syllogistic schema where the major premiss...

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