2 Diritto & Questioni Pubbliche 1 (2002)

handle is hein.journals/dirquesp2 and id is 1 raw text is: 

Diritti&questioni pubbliche - n.2 agosto 2002

                    Why   Is  Legal Reasoning Defeasible?*

                                   Juan  Carlos   Bay6n

Abstract. This paper analyses the claim that legal reasoning is defeasible, which is indeed a hallmark of some major
contributions to the theory of legal reasoning in recent times. Before addressing the question of what kind of logical
tools are needed to formalize defeasible reasoning, it must be explained why legal reasoning is supposed to be
defeasible in the first place. Some arguments to this effect are taken into account (having to do with the allocation of
burdens of proof in legal procedures, reasoning with incomplete information and the proper way of individuating
norms), but it is held that none of them really proves that legal reasoning cannot be reconstructed as a deductive
inference. The strongest argument to justify the claim that legal reasoning is defeasible seems then to be that all legal
norms turn out to be defeasible: but here this argument is disputed, trying to show that it would lead us to embrace
either wholesale indeterminacy or 'legal particularism', which is criticised as an untenable form of conceiving legal
justification. Finally, it is suggested that there is indeed some limited sense in which it could be said that legal
reasoning is defeasible (having to do with the idea that justification in law is a matter of coherence), but it is not
grounded on the possibility that legal norms themselves be defeasible as well, and especially it does not call in
question the subsumptive character of legal justification.

1. Legal   theory  behind a theory of legal reasoning

       Some   major  contributions  to the theory  of  legal reasoning  appeared   in recent
times  assume  as a seemingly  indisputable  starting point that it is defeasible.1 Of course,
the claim  that defeasibility is an essential trait of legal reasoning is by no means novel.2
But  only  recently has this claim  been  put forward  in a thorough   and systematic  way,
making   use of a set of notions and tools developed   in the field of artificial intelligence.
As  it is upheld nowadays,  the claim  seems  really to be twofold. First, on what could  be
called  its jurisprudential side, the contention  is that legal reasoning  does  have  some
distinctive features that  make  it non-monotonic.   Therefore,  any  version  of the  claim
includes  some  explanation  about what  is supposed  to be the real source  of defeasibility
in legal reasoning. And   secondly, on  its logical side, what is contended is that classical
logic is not suitable to formalize legal reasoning precisely because  it is defeasible. Then,
taking for granted  that we require new  logical tools to cope with defeasibility, the claim
is coupled  in its different versions with several proposals as to how the allegedly needed
non-standard  logic should  look like.
      Nevertheless,  the claim  has been  contested on  both sides.3 As for the logical one,
there  are  indeed  some   nagging   doubts  about  the  very  idea  of  working   out non-
monotonic logics. It is sometimes said that it makes no sense to speak of a non-
monotonic   'logic' unless one is prepared to accept  a non-monotonic   notion of inference.
However,   the  idea of a defeasible  conditional  as a new  kind  of logical connective   is
often  deemed   to  be flawed,  indeed   the product  of  conflating  a standard  notion  of
material  implication  with  the change  of  our premises   in a process  of rational belief
revision.   Hence,  this  purportedly  new   logical  connective  would   hardly  have   any
practical use, leading  to systems   of so-called  'non-monotonic   logic' computationally
inefficient. From  this point  of view  there is no  need  to deny  the genuine  interest of
framing   models  that  intend to  give formal   expression  to patterns  of rational belief
revision  in non-monotonic or default reasoning: what is stressed is that it would be
better not to think of them  as 'logics' properly said. Of  course, to this it can be replied
that all hinges on what  'a logic properly said' is supposed to be.  These  are complicated

* This essay has been published in A. Soeteman  (ed. by) Pluralism and Law, Kluwer Academic
Publishers, 2001


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