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1 CTC6, Educational Session 603 Artificial Intelligence in the Legal Environment A Legal Reasoning System on the Contract Law (CISG) Hajime YOSHINO Professor.

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Presentation on theme: "1 CTC6, Educational Session 603 Artificial Intelligence in the Legal Environment A Legal Reasoning System on the Contract Law (CISG) Hajime YOSHINO Professor."— Presentation transcript:

1 1 CTC6, Educational Session 603 Artificial Intelligence in the Legal Environment A Legal Reasoning System on the Contract Law (CISG) Hajime YOSHINO Professor of Law Meiji Gakuin University Faculty of Law Shirokanedai, Tokyo s

2 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.Legal reasoning system on CISG, LES-5 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 3 1.Introduction What is a legal reasoning system 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 4 Tasks of Judges and AI in Law s It is important task for a judge to decide what legal judgment should be made for a given case and to show how the judgment is justified. s A legal reasoning system as an artificial intelligence of law, which infers the legal state of affairs as conclusion from law and the facts of a case and shows clearly the deduction process, will be, therefore, a useful tool for the practice of judges.

5 5 Several approaches to legal reasoning system 1 rule based legal reasoning system British Nationality Act (Kowalski & Sergot), LES-2, LES-3 (Yoshino) 2 case based legal reasoning system HYPO(Ashley), GREBE(Branting) 3 hybrid reasoning system CABARET(Rissland & Skalak)

6 6 Limitations of the approaches Partial, narrow, separated legal subjects The whole deductive system of law is unclear The changes of legal relations in terms of time progress have not been enough clearly formalized Lack of legal theoretical basis

7 7 What is necessary to construct correct Legal Reasoning systems s In order to construct legal reasoning system it is necessary first to clarify the logical structure of the law system as a whole. s The legal state of affairs, which refers to the status of legal relations, changes according to the chronological progress of an event over time. We therefore must clarify such a logical model of law that enables us to deduce changes of legal relation according to time, regardless of any time point in given events from the beginning to the end. s The systematization of law, i.e., to present the law as a deductive system, has long been a central theme of legal theories, but previous studies did not succeed in presenting a legal system as deductive. s We need a sound and powerful logical theory of law.

8 8 The objectives of this paper s Logical Jurisprudence has succeeded in clarifying the logical structure of the law system in the above sense and on its basis we have developed a legal reasoning system entailing knowledge base of the CISG (United Nations Convention on Contracts of the International Sale of Goods). Our aim here is to present the essence of the clarification of the logical structure of contract law system by focusing on the CISG. s In this paper I would like to introduce you s what is Logical Jurisprudence, s how the structure of contract law is to be clarified, s what structure it has and s how we developed LES-5, a legal reasoning system of CISG and s How it works in fact in demonstration.

9 9 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.Legal reasoning system on CISG, LES-5 s 7.Conclusion

10 10 2. Case, query and solution s Case 8f (1) On April 3rd, 1997 A (Anzai), 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 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.

11 11 (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.

12 12 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

13 13 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;

14 14 Article 38 (1) The buyer must examine the goods, or cause them to be examined, within as short a period as is practicable in the circumstances. Article 39 (1) The buyer loses the right to rely on a lack of conformity of the goods if he does not give notice to the seller specifying the nature of the lack of conformity within a reasonable time after he has discovered it or ought to have discovered it. Article 45 (1) If the seller fails to perform any of his obligations under the contract or this Convention, the buyer may: (a) exercise the rights provided in articles 46 to 52; (b) claim damages as provided in articles 74 to 77. (2) The buyer is not deprived of any right he may have to claim damages by exercising his right to other remedies.

15 15 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.

16 16 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 $50,000 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 $50000 to A by 20 May, while A has right to require B to pat the price to A by 10 May. 4) On August 15th, 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.

17 17 Changes of legal Relationships (Fig. 3a)

18 18

19 19 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.Legal reasoning system on CISG, LES-5 s 7.Conclusion

20 20 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.

21 21 primitives: ssentence, 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

22 22 Legal Reasoning as a development of legal sentences (Fig.1)

23 23 Two types of legal Reasoning s Reasoning of legal justification Modus Ponens: A s Reasoning of legal discovery Abduction and induction falsification Modus Tollens: (

24 24 Legal Reasoning Structure (Fig.1)

25 25 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.Legal reasoning system on CISG, LES-5 s 7.Conclusion

26 26 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 (Fig.2)

27 27 Legal elementary and complex sentences s Elementary legal sentence the smallest unit of legal sentences. "one must drive a car under 100 km /hour on a highway A may require B to pay the price of $10000.

28 28 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).

29 29 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

30 30 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 …

31 31 Obligation of persons as ultimate normative state of affairs s Law ultimately prescribes the obligation of persons. s Peoples conduct is ultimately regulated by obligations given by object sentences. s What is that legal obligations exist ?

32 32 Obligation and the validity of legal object sentence

33 33 Contents s 1. Introduction s 2. Logical Jurisprudence s 3. Basic legal sentence concepts and structures s 4. Case, query and solution s 5. Logical structure of contract law regulating changes in legal relations s 6.Legal reasoning system on CISG, LES-5 s 7. Conclusion

34 34 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

35 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.

36 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)

37 37 Changes of legal Relationships (Fig. 3a)

38 38 Fig. 4

39 39 Fig.5

40 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.

41 41 Changes of legal Relationships ( Fig. 3b)

42 Logical structure of contract law deciding termination of obligations The validity of elementary legal sentence is terminated if the complex legal sentence is terminated.

43 43 Changes of legal Relationships ( Fig. 3b)

44 Logical structure of contract law deciding termination of obligations The validity of elementary legal object sentences is terminated when the obligation is fulfilled.

45 45 Changes of legal Relationships (Fig. 3a)

46 46 Contents s 1. Introduction s 2. Logical Jurisprudence s 3. Basic legal sentence concepts and structures s 4. Case, query and solution s 5. Logical structure of contract law regulating changes in legal relations s 6.Legal reasoning system on CISG, LES-5 s 7. Conclusion

47 47 6. Legal reasoning system on the CISG, LES5 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 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 systematization of law in LES5 might prove the legitimacy and powerfulness of LJ.

48 48 Demonstration of LES-5 Switch to Netscape Navigator !

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92 92 Contents s 1. Introduction s 2. Logical Jurisprudence s 3. Basic legal sentence concepts and structures s 4. Case, query and solution s 5. Logical structure of contract law regulating changes in legal relations s 6. Legal reasoning system on CISG, LES-5 s 7. Conclusion

93 93 7. Conclusion A Legal reasoning system (LES) will be useful for judges to get proposals of the solutions of cases and their justification. Legal reasoning system needs a good, general theory of Law. LJ could afford the sound basis of LES. LJ starts from three primitives: legal sentences, the validity and inference rules. It identifies the three sorts of legal sentences: rule and fact sentences, object and meta sentences, elementary and complex sentences. 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 on CISG, LES5 has been developed. As the basic deductive structure of law as a whole is clarified and a LES on CISG is made on the basis, we could go further to develop LES on various law fields and to integrate them in the future. 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.

94 94 I would conclude this lecture with most important words: Thank you!


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