1 Logical Jurisprudence Towards the Science of Law Through AI in Law Workshop on  Logical Jurisprudence and Legal Informatics  Sep.30./ October 1. 1999,

1 Logical Jurisprudence Towards the Science of Law Through AI in Law Workshop on  Logical Jurisprudence and Legal Informatics  Sep.30./ October 1. 1999, Vienna  Hajime YOSHINO  1-2-37 Shirokanedai, 108-8636 Tokyo  yoshino@law.meijigakuin.ac.jp yoshino@law.meijigakuin.ac.jp s http://www.meijigakuin.ac.jp/~yoshino

2 Contents s 1. Introduction s 2. Case, query and solution s 3. What is Logical Jurisprudence ? s 4. Basic legal sentence concepts and structures s 5. Logical structure of contract law regulating changes of legal relations s 6. Realizing a legal reasoning system on the CISG s 7. Conclusion Hajime Yoshino: Object of this paper Problem (Case, query and solution) and Jurisprudence for it Necessity of Sound and Efficient Jurisprudence Development of Logical Jurisprudence Hajime Yoshino: Object of this paper Problem (Case, query and solution) and Jurisprudence for it Necessity of Sound and Efficient Jurisprudence Development of Logical Jurisprudence Hajime Yoshino: Birth and Development of Logical Jurisprudence (LJ as a front for science of law) LJ as a applied logic to law (LJ as a realistic theory of law) the concept of law in LJ Primitives of LJ Legal Reasoning in terms of LJ Hajime Yoshino: Birth and Development of Logical Jurisprudence (LJ as a front for science of law) LJ as a applied logic to law (LJ as a realistic theory of law) the concept of law in LJ Primitives of LJ Legal Reasoning in terms of LJ

3 1. Introduction  To found and establish the law (legal science) as a real science has been a long dream of many legal scholars. It has been very difficult to establish law as a science. However, we are now confronting with a new breach to the development of legal science as a real science, which is going to be provided by Logical Jurisprudence (LJ).  One of the tasks of legal scholar who tried to found the legal science as a science has been to systematize the law. In other words, they have tried to clarify the systematical structure of law or to show the law as a deductive system. But no one has been succeeded in it yet.  However recently, Logical Jurisprudence (LJ) in cooperation with AI approach to law has made a big progress on it.  In this paper I would like to present you the basic framework of LJ and a logical model of law based on LJ, which enables us to clarify the structure of law and to systematize the law as a deductive system, not only on an abstract level but also on a concrete level to solve a real complex legal problem. I would like to show you an application result of LJ to the CISG and LES-5, an expert system on the law, which could prove the effective ness of LJ. Hajime Yoshino: try to show what kind of logical structure legal knowledge has in order that a lawyer deduces such resolutions as results of legal reasoning. This study presents such a model based on Logical Jurisprudence, in which the relationship between legal sentences and legal meta sentences that regulate the validity of the former plays a definitive role. The model is applied to the United Nations Convention on Contracts for the International Sale of Goods (CISG) to develop a deductive knowledge base system. The deductive structure of the contract law is clarified so that appropriate answers can be deduced to questions about the legal state of affairs at any time point as a result of the application of CISG provisions to a concrete case. It is necessary for the science of law as well as AI in Law from which a legal judgement can be justified as a conclusion of logical deduction together with relevant facts. As the legal state of affairs changes according to the time progress of an event, a clarified logical model of law is necessary to enable us to deduce the changes among legal relationships over time from the beginning to the end of a case. Hajime Yoshino: try to show what kind of logical structure legal knowledge has in order that a lawyer deduces such resolutions as results of legal reasoning. This study presents such a model based on Logical Jurisprudence, in which the relationship between legal sentences and legal meta sentences that regulate the validity of the former plays a definitive role. The model is applied to the United Nations Convention on Contracts for the International Sale of Goods (CISG) to develop a deductive knowledge base system. The deductive structure of the contract law is clarified so that appropriate answers can be deduced to questions about the legal state of affairs at any time point as a result of the application of CISG provisions to a concrete case. It is necessary for the science of law as well as AI in Law from which a legal judgement can be justified as a conclusion of logical deduction together with relevant facts. As the legal state of affairs changes according to the time progress of an event, a clarified logical model of law is necessary to enable us to deduce the changes among legal relationships over time from the beginning to the end of a case. yoshino: This paper presents at first a hypothetical legal problem, queries on it and the resolutions. It shows then what LJ is and it introduces basic concepts of legal sentences according which LJ enables us to constitute a logical system of law. On this basic model, this paper clarifies the logical structure of law focusing on contract law which regulates change in legal relations. This paper refers to LES5 as a realization of legal reasoning develop by us on the basis of LJ. It concludes suggesting further possibilities of LJ. yoshino: This paper presents at first a hypothetical legal problem, queries on it and the resolutions. It shows then what LJ is and it introduces basic concepts of legal sentences according which LJ enables us to constitute a logical system of law. On this basic model, this paper clarifies the logical structure of law focusing on contract law which regulates change in legal relations. This paper refers to LES5 as a realization of legal reasoning develop by us on the basis of LJ. It concludes suggesting further possibilities of LJ.

4 Contents s 1. Introduction s 2. Case, query and solution s 3. What Is Logical Jurisprudence s 4. Basic legal sentence concepts and structures s 5. Logical structure of contract law regulating changes in legal relations s 6. Realizing a legal reasoning system s 7.Conclusion

5 2. Case, query and solution s Case 8f  1) On April 3rd, 1998), a farming machine maker in New York, sent a letter to the branch office in Hamburg of B (Bernard), a Japanese trading company. The content of the letter was: A sells B a set of agricultural machines which is composed of a tractor and a rake and the price of the tractor is $50000; A delivers the machine to B by May 10 th, B must pays the price of the system to A by May 20 th and the agricultural machinery will be carried by an American freight vessel.  2) On April 8th, the letter reached the letter box of B ’ s branch office in Hamburg.  3) On April 9th, B made a telephone A (Anzai call to A. “ I accept your offer. However, I want you to carry the machine by a Japanese containership ”  4) On May 1st, A delivered the farming machine to a Japanese container ship at the port of New York.

6  5) On May 31, the machine was delivered to the branch office in Hamburg.  6) On June 5th, B examined the machine.  7) On May, 10th B paid the price to A.  8) On August 10th, the machine proved to be operating out of order because of a bad connection gear. B immediately gave the notice to A specifying the nature of the lack of conformity.  9) On September 1st, B asked A to repair the lack of conformity of the machine within one month. A did not repair the non- conformity until 1 October.  10) On October 10th, B declared the avoidance of the contract.  11) On December 10th, A recovered the damage and B restituted the machine delivered by A.  12) On December 20, A restituted the price paid by B.

7 Queries  At each of the points of time indicated below, what is the legal relation that exists between A and B?  1: April 5th  2: April 15th  3: May 5th  4: August 15th  5: September 15th  6: October 5th  7: November 15th  8: December 15th  9: December 25th

8 CISG Articles  The following articles of the CISG apply to the case:  Article 15(1) An offer becomes effective when it reaches the offeree.  (2) An offer, even if it is irrevocable, may be withdrawn if the withdrawal reaches the offeree before or at the same time as the offer.Article 16(1) Until a contract is concluded an offer may be revoked if the revocation reaches the offeree before he has dispatched an acceptance.  Article 18(2) An acceptance of an offer becomes effective at the moment the indication of assent reaches the offeror. ….  Article 23  A contract is concluded at the moment when an acceptance of an offer becomes effective in accordance with the provisions of this Convention.  Article 31  If the seller is not bound to deliver the goods at any other particular place, his obligation to deliver consists:  (a) if the contract of sale involves carriage of the goods - in handing the goods over to the first carrier for transmission to the buyer;

9  Article 46  (1) The buyer may require performance by the seller of his obligations unless the buyer has resorted to a remedy which is inconsistent with this requirement.  (2) If the goods do not conform with the contract, the buyer may require delivery of substitute goods only if the lack of conformity constitutes a fundamental breach of contract and a request for substitute goods is made either in conjunction with notice given under article 39 or within a reasonable time thereafter.  (3) If the goods do not conform with the contract, the buyer may require the seller to remedy the lack of conformity by repair, unless this is unreasonable having regard to all the circumstances. A request for repair must be made either in conjunction with notice given under article 39 or within a reasonable time thereafter.  Article 49  (1) The buyer may declare the contract avoided:  (a) if the failure by the seller to perform any of his obligations under the contract or this Convention amounts to a fundamental breach of contract; or  (b) in case of non-delivery, if the seller does not deliver the goods within the additional period of time fixed by the buyer in accordance with paragraph (1) of article 47 or declares that he will not deliver within the period so fixed.

10 Solutions  1) On April 5th, there is no legal relation between the seller A (Anzai) and the buyer B (Bernard)  2) On April 15th, A has a duty to deliver the farming machine to B by May 10th and B has a duty to pay the price to A by May 20th, while B has right to require A to deliver the goods to B and A has the right to require B to pay the price to A by May 10th.  3) On May 5th, B has a duty to pay the price to A by 20 May, while A has right to require B to pay the price to A by 10 May.  4) On August 1th, A has a duty to recover the damage, while B has right to claim A the damage and B has right to require A to repair the machine.  5) On September 15th, A has a duty to recover the damage and a duty to repair the machine, while B has right to claim A the damage and B has the right to require A to repair the machine which is restricted to exercise.  6) On October 5th, A has a duty to recover the damage and a duty to repair the machine, while B has right to claim A the damage, B has right to require A to repair the machine and B has a right to declare the contract avoided.  7) On November 15th, A has a duty to recover the damage and a duty to restitute the price paid by B, and B has a duty to restitute the machine delivered by A, while B has a right to claim A the damage and a right to require A to restitute the price, and A has right to require B to restitute the machine.  8) On December 15th, A has a duty to restitute the price paid by B, while B has right to require A to restitute the price.  9) On December 25th, there is not legal relation between A and B on the contract.

11 Changes of legal Relationships (Fig. 3a)

14 3. What Is Logical Jurisprudence (LJ) s Concept of logical jurisprudence Logishe Rechts Lehre A developed form of “legal logic” (Juristische Logik) Naming is done by Hajime Yoshino (in 1991 at University of Pittsburgh School of Law).

15 primitives: s “sentence,” LJ consider that norm as a meaning does not exist. LJ starts from sentences. s “validity” of sentence legal validity as legal truth s “inference rule.” Modus Ponens: （（ A → Ｂ）＆Ａ） → Ｂ

16 Legal Reasoning as a development of legal sentences (Fig.1)

17 s Statute Legal Conclusion Interpretation 2 Confirmed Fact Described Fact Events Interpretation 1 Legal Principle Common Sense Set Discovery Legal Reasoning as a development of legal sentences (Fig.1a) Go to and back of Glance Purpose of Law Purpose of Law Concrete Justice Concrete Justice Justification

18 IOI Becomes effect.←it reaches Addressee A contract is concluded IOI comes under Addressee’s control ← it reaches his post box A’s offer reached B A’s offer reached B’s post box Events IOI reaches addressee.←it comes under his control A contract is concluded← offer become effective and acceptance becomes effective Indication Of Intention←offer Set Discovery Legal Reasoning Structure-A Case of Contract Conclusion Go to and back of Glance Purpose of Law Purpose of Law Concrete Justice Concrete Justice Justification

19 Two types of legal Reasoning s Reasoning of legal justification Modus Ponens: （（ A → Ｂ）＆Ａ） → Ｂ s Reasoning of legal discovery Abduction and induction falsification ： Modus Tollens: （ ( Ａ → Ｂ）＆～Ｂ） → ～Ａ

20 Legal Reasoning as a development of legal sentences (Fig.1)

22 4. Basic legal sentence concepts and structures s Legal rule and fact sentences s Legal object and meta sentences s Legal elementary and complex sentences s Existence of an obligation and the validity of the legal object sentence

23 Legal rule and fact sentences s Legal rule sentences: “ ∀ X{a(X) ← b(X)}”. legal consequence ←legal requirement “ ∀ X{become_effective(offer(X,A),T) ← reach(offer(X,A),offeree(B,X),T)}” s Legal fact sentences: “b(x1)”. reach(offer(o1,anzai),offeree(bernard,o1),4_05).

24 Legal elementary and complex sentences s Elementary legal sentence the smallest unit of legal sentences: An element of contract or statute "one must drive a car under 100 km /hour on a highway” s Complex legal sentence a sentence named for a group of legal sentences code, contract, a section of statute, an article “the United Nations Convention on Contracts for the International Sale of Goods,” “a contract for sale of a farming machine between A and B on October 8. 1997.”

25 Legal object and meta sentences s A legal object sentence describes obligations of a person “B must pay A the price of $10000” s A legal meta sentence prescribes about legal sentences It describes the validity of a legal sentence. “(1) This Convention applies to contracts of sale of goods between parties whose places of business are in different States : (a) when the States are Contracting States; or … ”

26 Obligation of persons as ultimate normative state of affairs s Law ultimately prescribes the obligation of persons. s People’s conduct is ultimately regulated by obligations given by object sentences. s What is that legal obligations exist ?

27 Obligation and the validity of legal object sentence

29 5. Logical structure of contract law regulating changes in legal relations s 5.1 Legal rule sentences deciding that legal sentences are valid. s 5.2 Logical structure of contract law deciding accrual of obligation s 5.3 Logical structure of contract law deciding termination of obligations

30 5.1 Legal rule sentences deciding that legal sentences are valid.  Fundamental legal meta rule sentence is valid to confirm that legal sentences are valid:  (0) A legal sentence S is valid at the time T ←  S becomes valid at time T1 before T ＆  S is not terminated until T The validity of this fundamental legal meta rule is described as a fact. Or it is presupposed that it is always valid.

31 5.2 Logical structure of contract law deciding accrual of obligation  The accrual of validity of a complex legal sentence follows the accrual of validity of elementary legal sentences which belong to it.  (r01) become_valid(ES,G,T) <-  element_complex_sentence(ES,CS) & become_valid(CS,G,T)

33 Fig. 4

34 Fig.5

35 5.2.2 The accrual of the validity of a legal object sentence by exercising the right  The accrual of validity of the elementary legal sentence by itself can be regulated.  (3AA2) "A legal sentence 'X has an obligation to do Z' becomes valid at time T,  if a legal sentence 'Y has a right to require X to do Z' is valid, and Y exercises the right to require X to do Z at time T. ”  (rCISG46): “ The buyer has a right to require the seller to remedy the lack of conformity by repair ” becomes valid,  if the goods do not conform with the contract.

36 Changes of legal Relationships ( Fig. 3b’)

37 5.3 Logical structure of contract law deciding termination of obligations  The termination of an obligation means that the validity of legal object sentence describing the obligation is terminated.  There are two ways to terminate the validity of legal object sentences

38 5.3.1 Termination of elementary legal sentences through the termination of the complex sentence  The validity of elementary legal sentences is terminated if the complex sentence to which they belong is terminated.  The validity of elementary sentences of a contract are terminated if the validity of the contract as a complex legal sentence is terminated.

39 Changes of legal Relationships ( Fig. 3b’)

40 5.3.2 Termination of elementary legal object sentences with fulfillment of the obligation  (mr4b) The validity of elementary legal object sentences is terminated when the obligation is fulfilled.

43 6. Realizing a legal reasoning system on the CISG s The clarification of logical structure of the contract law is applied to construct a legal reasoning system on the CISG (LES5). s The relevant knowledge is written at first in the form of logical flow chart and the represented in CPF in Knowledge Base. s The inference system and explanation system is written in logic programming. s The inference engine produces html format text as a result of inference, so that one can follow the reasoning process through internet. s The system can deduce states of legal relationships at any time point of cases as results of the application of the CISG to concrete cases. s It can explain the reason of the deduction. s The system could provide the basis of further development of LES as a total system. s The systematization of law in LES5 might prove the legitimacy and powerfulness of LJ.

44 Demonstration of LES-5 Switch to Netscape Navigator !

46 7. Conclusion  LJ starts from three primitives: legal sentences, the validity and inference rules.  LJ identifies the three sorts of legal sentences: rule and fact sentences, object and meta sentences, elementary and complex sentences and.  On the basis of these conceptions, the basic structure of legal knowledge has been clarified.  By taking up the CISG as an example, the structure of contract law is thus clarified in terms of LJ.  The study results of knowledge clarification by LJ are put into computer and a legal reasoning system LES5 has been developed, which could prove the legitimacy and power of LJ.  I would suggest that LJ could develop the science of law cooperating with artificial intelligence approach to law. yoshino: On these way of formalization, the change of legal relations is described as a change of the validity of legal object sentences that describes obligations. On the formalization, the fundamental legal meta rule sentence is confirmed under which every other legal meta rules are systematized. Thus I clarified the logical structure of contract law system which can deductively prove the change of the legal relation along with the progress of events. yoshino: On these way of formalization, the change of legal relations is described as a change of the validity of legal object sentences that describes obligations. On the formalization, the fundamental legal meta rule sentence is confirmed under which every other legal meta rules are systematized. Thus I clarified the logical structure of contract law system which can deductively prove the change of the legal relation along with the progress of events.

47 I would like to conclude this lecture with most important words: TThank you! DDanke schoene! HHajime YOSHINO yyyy oooo ssss hhhh iiii nnnn oooo @@@@ llll aaaa wwww.... mmmm eeee iiii jjjj iiii gggg aaaa kkkk uuuu iiii nnnn.... aaaa cccc.... jjjj pppp shshttp://www.meijigakuin.ac.jp/~yoshino

1 Logical Jurisprudence Towards the Science of Law Through AI in Law Workshop on  Logical Jurisprudence and Legal Informatics  Sep.30./ October 1. 1999,

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1 Logical Jurisprudence Towards the Science of Law Through AI in Law Workshop on  Logical Jurisprudence and Legal Informatics  Sep.30./ October 1. 1999,

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