CTC 6 Educational Session 603 Artificial Intelligence in

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CTC 6, Educational Session 603 Artificial Intelligence in the Legal Environment A Legal Reasoning System on the Contract Law (CISG) s Hajime YOSHINO s Professor of Law s Meiji Gakuin University Faculty of Law s 1 -2 -37 Shirokanedai, 108 -8636 Tokyo s yoshino@law. meijigakuin. ac. jp s http: //www. meijigakuin. ac. jp/~yoshino 1

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

yoshino: This structure legal ogicalpaper presents at first a hypothetical legal problem, tqueries on deduces the resolutions. It shows then what LJ a lawyer it and such is and it introduces basic concepts of legal sentences legal reasoning. according which Logical model based on LJ enables us to constitute a logical On this basic model, this paper clarifies esystem of law. between relationship the sentences that meta logical structure of law focusing on contract law which regulates he former plays achange in legal relations. This paper lrefers to LES 5 as a realization of legal reasoning develop is applied to the by us on the basis on Contracts for theof LJ. It concludes suggesting further spossibilities of LJ. (CISG) to develop a ystem. The deductive law is clarified so that deduced to questions ffairs at any time point tion of CISG provisions 1. Introduction What is a legal reasoning system ience of law as well as nt can be justified as a ction together with gal state of affairs ime progress of an model of law is deduce the changes among ime from the beginning 3

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 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. 4

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) 5

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 6

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 s We need a sound and powerful logical theory of law. 7

The objectives of this paper s s s 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. In this paper I would like to introduce you what is Logical Jurisprudence, how the structure of contract law is to be clarified, what structure it has and how we developed LES-5, a legal reasoning system of CISG and How it works in fact in demonstration. 8

Contents s s s 1. Introduction 2. Case, query and solution 3. What Is Logical Jurisprudence 4. Basic legal sentence concepts and structures 5. Logical structure of contract law regulating changes in legal relations 6. Legal reasoning system on CISG, LES-5 7. Conclusion 9

2. Case, query and solution s Case 8 f ( 1) On April 3 rd, 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 8 th, the letter reached the letter box of B’s branch office in Hamburg. ( 3) On April 9 th, B made a telephone call to A. “I accept your offer. However, I want you to carry the machine by a Japanese 10 containership”

( 5) On May 31, the machine was delivered to the branch office in Hamburg. ( 6) On June 5 th, B examined the machine. ( 7) On May, 10 th B paid the price to A. ( 8) On August 10 th, 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 1 st, B asked A to repair the lack of conformity of the machine within one month. A did not repair the nonconformity until 1 October. ( 10) On October 10 th, B declared the avoidance of the contract. ( 11) On December 10 th, A recovered the damage and B restituted the machine delivered by A. ( 12) On December 20, A restituted the price paid by B. 11

Queries s s At each of the points of time indicated below, what is the legal relation that exists between A and B? 1: April 5 th 2: April 15 th 3: May 5 th 4: August 15 th 5: September 15 th 6: October 5 th 7: November 15 th 8: December 15 th 9: December 25 th 12

s s s s 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 13 consists:

s s s s s 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. 14

s s s s 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 15 (b) in case of non-delivery, if the seller does not deliver the goods within the additional period of time

Solutions s s s s 1) On April 5 th, there is no legal relation between the seller A (Anzai) and the buyer B (Bernard) 2) On April 15 th, A has a duty to deliver the farming machine to B by May 10 th and B has a duty to pay the price $50, 000 to A by May 20 th, 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 10 th. 3) On May 5 th, 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 15 th, 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 15 th, 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 5 th, 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 15 th, 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. 16 8) On December 15 th, A has a duty to restitute the price paid by

Changes of legal Relationships (Fig. 3 a) 17

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. 20

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: （（ →Ｂ）＆Ａ） A →Ｂ 21

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

Two types of legal Reasoning s Reasoning of legal justification • Modus Ponens: （（ →Ｂ）＆Ａ） A →Ｂ s Reasoning of legal discovery • Abduction and • induction • falsification： Modus Tollens: （(Ａ→Ｂ）＆～Ｂ）→～Ａ 23

Legal Reasoning Structure (Fig. 1) 24

4. Basic legal sentence concepts and structures s s Legal rule and fact sentences Legal object and meta sentences Legal elementary and complex sentences Existence of an obligation and the validity of the legal object sentence (Fig. 2) 26

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. ” 27

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(x 1)”. • reach(offer(o 1, anzai), offeree(bernard, o 1), 4_05). 28

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. ” 29

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 … ” 30

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

Obligation and the validity of legal object sentence 32

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

5. Logical structure of contract law regulating changes in legal relations s 5. 1 Legal rule sentences deciding that legal sentences are valid. 5. 2 Logical structure of contract law deciding accrual of obligation 5. 3 Logical structure of contract law deciding termination of obligations 34

5. 1 Legal rule sentences deciding that legal sentences are valid. s s 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 　　 ← 　　 becomes valid at time T 1 before T S ＆　　 is not terminated until T S • The validity of this fundamental legal meta rule is described as a fact. Or it is presupposed that it is always valid. 35

5. 2 Logical structure of contract law deciding accrual of obligation s The accrual of validity of a complex legal sentence follows the accrual of validity of elementary legal sentences which belong to it. s (r 01) become_valid(ES, G, T)

Changes of legal Relationships (Fig. 3 a) 37

Fig. 4 38

Fig. 5 39

5. 2. 2 The accrual of the validity of a legal object sentence by exercising the right s The accrual of validity of the elementary legal sentence by itself can be regulated. s (3 AA 2) "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. ” s s s (r. CISG 46): “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. 40

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

5. 3 Logical structure of contract law deciding termination of obligations s The validity of elementary legal sentence is terminated if the complex legal sentence is terminated. 42

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

5. 3 Logical structure of contract law deciding termination of obligations s The validity of elementary legal object sentences is terminated when the obligation is fulfilled. 44

Changes of legal Relationships (Fig. 3 a) 45

6. Legal reasoning system on the CISG, LES 5 s s s The clarification of logical structure of the contract law is applied to construct a legal reasoning system on the CISG (LES 5). The relevant knowledge is written at first in the form of logical flow chart and the represented in CPF in Knowledge Base. The inference system and explanation system is written in logic programming. 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. It can explain the reason of the deduction. The systematization of law in LES 5 might prove the legitimacy and powerfulness of LJ. 47

Demonstration of LES-5 Switch to Netscape Navigator ! 48

yoshino: 7. Conclusion On these way of formalization, the change of legal relations is s A Legal change of system (LES) described as a reasoning the judges to object sentences validity of legal get proposals of the that and their justification. describes obligations. will be useful for solutions of cases Legal reasoning system needs a good, general theory of Law. LJ could afford the sound basis of LES. On the formalization, the s LJ starts meta three primitives: legal sentences, fundamental legal from rule sentence the validity and inference It identifies the is confirmed under which every other rules. legalthree rules areof legal sentences: rule and fact meta sorts systematized. sentences, object and meta sentences, elementary and Thus complex sentences. I clarified the logical structure of contractof these conceptions, the basic s On the basis law system whichstructure of legal the can deductively prove knowledge has been clarified. change of the legal relation along s with By taking up the CISG as an example, the structure the progress of events. of contract law is thus clarified in terms of LJ. s The study results of knowledge clarification by LJ are put into computer and a legal reasoning system on CISG, LES 5 has been developed. s As the basic deductive structure of law as a whole is clarified and a LES on CISG is made on the 93 basis, we could go further to develop LES on various s

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