1 logical jurisprudence towards the science of law through ai in law workshop on logical...

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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

[email protected] http://www.meijigakuin.ac.jp/~yoshino

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Contents 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 of legal relations 6. Realizing a legal reasoning system on the

CISG 7. Conclusion

Hajime Yoshino:

Object of this paperProblem (Case, query and solution) and Jurisprudence for itNecessity of Sound and Efficient JurisprudenceDevelopment of Logical Jurisprudence

Hajime Yoshino:


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 LJPrimitives of LJLegal Reasoning in terms of LJ

Hajime Yoshino:


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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 Lawfrom 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 Lawfrom 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.

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Contents 1. Introduction 2. Case, query and solution 3. What Is Logical Jurisprudence 4. Basic legal sentence concepts and


changes in legal relations 6. Realizing a legal reasoning system 7.Conclusion

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2. Case, query and solution 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 10th, B must pays the price of the system to A by May 20th 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.

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4) On May 1st, A delivered the farming machine to a Japanese container ship at the port of New York.

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.

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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

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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;

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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.

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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.

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Changes of legal Relationships (Fig. 3a)

５月10日までに

引渡す義務がある

15４／

５／５

Seller・Ａ

A has aduty todeliverthe goods

B has aduty topay theprice toA by

May 10.

B mayrequireA to

deliverthegoods

Buyer・ＢＢＡ

Events＜＞ Validity of Legal Sentence＜＞ Query＜＞ Answer＜＞

query(2)

query(3)

Offer iseffective

query(1)

４／５

Offer be-comes valid

B pays the price

The goods is delivered to B

B examines the goods

A has a duty todeliverthe goodswhich conformsto the contract

A mayrequire

B to paythepricebyMay10th.

Accept. be-comes validContract becomes valid

Offer reaches to B

Acceptance reaches to A

hands over the Ａgoods to the first carrier Japanese Container Ship

duty to deli-ver the goods

There is nolegal relation

right to require todeliver the goods

right to requireto pay the price

duty ot paythe pride

duty to paythe price

right to paythe price

４／８

４／９

５／１

10５／

31５／

６／５

Figure 3: The Changes of Legal Relation

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A has a duty todeliver

the goodswhich

conformsto the contract

15９／

10／５

The additional period expired.

right to reqire to repair

right to claim damage


right to require to repair

( restricted )

right to requireto repairB may

declare the

contract avoided.

The right to claim

to repair is

restricted.

Exercise of claim to repair.

B may require A to repair

the machine.

query(4)

query(5)

query(6) right to claim

damage

right to declaincontract avoided

B declared the contract avoided.

claim to restituteA the machiner

11 15／ query(7)



claim to restituteB the price

12 25／

query(8)

query(9)

９／１

8 10／

９／１

10／１

10 10／

12 10／

12 20／

12 15／

15８／

A has a duty to recover the damage for B.

B may claim A the the damage.

The machine is operatingout of order

B noticed to A specifyingthe nature of the lack of

conformity

B asked A to repair the machine within one month.

A restituted theprice paid by B.

A recovered the damge.B restituted the machine.

duty to reco-ver the damage

duty to repairthe machine




duty to resti-tute the price


duty to resti-tute machine



B mayrequire Ato repair

the machine

B has a duty to

restitute A the

machine.

B mayclaim A

torestitutethe pricepaid by B

A may claim B to

restitute the

machine delivered

by A.

A hasa duty torestitute

Bthe pricepaid by B

Exerise of right to declare contract avoided

B has a duty to repair the machine.

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Contents 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


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3. What Is Logical Jurisprudence 　 (LJ)

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).

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primitives: “sentence,”　

• LJ consider that norm as a meaning does not exist.

• LJ starts from sentences. “validity”　of　sentence

• legal　validity　as　legal　truth “inference　rule.”

•Modus　Ponens:　（（ A　→ Ｂ）＆Ａ）→Ｂ

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

Statute

Legal Rule Sentences

Fact Sentence

Described Fact

Events

Legal Judgement Sentence

Set

Set

Set

Set

Purposeof Law

Go to and back of Glance

hard

soft

Legal Principle

Interpretation１(case; general opinion）

Common Sense ofLegal Concepts

Interpretation 1.1for a concrete case（）

Justification

Discovery

Confirmed fact

Legal ConclusioonConcreeteJustice

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ssStatute

Legal Conclusion

Interpretation 2

Confirmed Fact

Described Fact

Events

Interpretation 1

Legal Principle

Common Sense

Set

Set

Set

Set

Discover

y

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


Purpose of Law

Purpose of Law

ConcreteJustice

ConcreteJustice

Justificatio

n

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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

Set

Set

Set

Discover

y

Legal Reasoning Structure-A Case of Contract Conclusion

Go to and back

of Glance

Purpose of Law

Purpose of Law

ConcreteJustice

ConcreteJustice

Justificatio

n

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Two types of legal Reasoning

Reasoning of legal justification•Modus　Ponens:　（（ A　→ Ｂ）＆Ａ）→Ｂ

Reasoning of legal discovery• Abduction and

• induction

• falsification 　： Modus Tollens: （ ( Ａ→Ｂ）＆～Ｂ）→～Ａ

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

Statute

Legal Rule Sentences

Fact Sentence

Described Fact

Events

Legal Judgement Sentence

Set

Set

Set

Set

Purposeof Law


hard

soft

Legal Principle

Interpretation１(case; general opinion）

Common Sense ofLegal Concepts

Interpretation 1.1for a concrete case（）

Justification

Discovery

Confirmed fact

Legal ConclusioonConcreeteJustice

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Contents 1. Introduction 2. Case, query and solution 3. What Is Logical Jurisprudence 4. Basic legal sentence concepts and



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4. Basic legal sentence concepts and structures

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

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Legal rule and fact sentences

　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)}”

Legal fact sentences:　• “b(x1)”.• reach(offer(o1,anzai),offeree(bernard,o1),4_05).

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Legal elementary and complex sentences

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”　 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.”

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Legal object and meta sentencesA　legal object sentence　describes　obligations　of　a　person• 　“B　must　pay　A　the　price　of　$10000”　

　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　…　”

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Obligation of persons as ultimate normative state of affairs

Law ultimately prescribes the obligation of persons. People’s conduct is ultimately regulated by obligations

given by object sentences.

What is that legal obligations exist ?

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Obligation and the validity of legal object sentence

Figure 2: The Existence of an Obligation and the validity of the object legal sentence

X is obliga-tory

Oligation Xturns up

Obligation Xis terminated

"X is obligatory" is valid

There is no obligation.

There is no obligation

No legal object sentenceis valid.

No legal object sentenceis valid.

events legal bject sentence legal meta sentence

Obligation X exists.

"X is ob-ligatory"is valid.

"Xi is obligatory"becomes valid

"Xi is obligatory"is terminated

event1

event2

t0

t1

T

t2

t3

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structures 5. Logical structure of contract law

regulating changes of legal relations 6. Realizing a legal reasoning system on the

CISG 7. Conclusion

Hajime Yoshino:


Hajime Yoshino:


Hajime Yoshino:


Hajime Yoshino:


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5. Logical structure of contract law regulating changes in legal

relations 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

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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.

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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)

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15４／

５／５

Seller・Ａ



May 10.

B mayrequireA to

deliverthegoods

Buyer・ＢＢＡ


query(2)

query(3)

query(1)

４／５

B pays the price




A mayrequire


Offer reaches to B










４／８

４／９

５／１

10５／

31５／

６／５


Offer iseffective

Contract becomes validAccept. be-comes valid


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Fig. 4

Ｔ＝Ｔ１

Yes(true)

Yes(true)

Yes(true)

No(false)

No(false)

No(false)

No(false)

No(false)

Yes(true)

Figure 4: 3AA1B A contract becomes valid.

[3AA1BA] A contrac is concludedat time T1 before time T

[3AA1BD] Contract entailsa condition of the validity

[3AA1BE] The conditionis sutisfied at time T

[3AA1BC] The begning time has come at T

[3AA1BC] Contract entails the begning time

[3AA1BB] not(The contract is invalid at T）

[3AA1B] A contract S becomes valid at time

[~3AA1B]not(A contract S becomes valid at time)

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Fig.5

yes

yes

[2AB] An acceptance of the offerbecomes valid at time T.

no

no

[2A] A contract the content ofwhich S is concluded at time T.

[~2A] not(A contract the content ofwhich is S is concluded at time T)

[2AA] An offer of a contract thecontent which is S is valid at time

Figure 5: [2A]Contract is conluded

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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.

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Changes of legal Relationships (Fig. 3b’)


the goodswhich


15９／

10／５






( restricted )


declare the

contract avoided.

The right to claim

to repair is

restricted.


the machine.

query(4)

query(5)


damage




11 15／ query(7)




12 25／

query(8)

query(9)

９／１

8 10／

９／１

10／１

10 10／

12 10／

12 20／

12 15／

15８／





conformity















the machine

B has a duty to

restitute A the

machine.

B mayclaim A


A may claim B to

restitute the

machine delivered

by A.


Bthe pricepaid by B




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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

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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.

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Changes of legal Relationships (Fig. 3b’)


the goodswhich


15９／

10／５






( restricted )


declare the

contract avoided.

The right to claim

to repair is

restricted.



the machine.

query(4)

query(5)


damage




11 15／ query(7)




12 25／

query(8)

query(9)

９／１

8 10／

９／１

10／１

10 10／

12 10／

12 20／

12 15／

15８／





conformity















the machine

B has a duty to

restitute A the

machine.

B mayclaim A


A may claim B to

restitute the

machine delivered

by A.


Bthe pricepaid by B



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.

41




15４／

５／５

Seller・Ａ



May 10.

B mayrequireA to

deliverthegoods

Buyer・ＢＢＡ


query(2)

query(3)

Offer iseffective

query(1)

４／５


B pays the price




A mayrequire


Accept. be-comes validContract becomes valid

Offer reaches to B










４／８

４／９

５／１

10５／

31５／

６／５


42



changes of legal relations 6. Realizing a legal reasoning system on

the CISG 7. Conclusion

Hajime Yoshino:


Hajime Yoshino:


Hajime Yoshino:


Hajime Yoshino:


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6. Realizing a legal reasoning system on the CISG

The clarification of logical structure of the contract law is applied to construct a legal reasoning system on the CISG (LES5).

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 inference engine produces html format text as a result of inference, so that one can follow the reasoning process through internet.

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 system could provide the basis of further development of LES as

a total system. The systematization of law in LES5 might prove the legitimacy and

powerfulness of LJ.

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Demonstration of LES-5

Switch to Netscape Navigator !

45



changes of legal relations 6. Realizing a legal reasoning system on the

CISG 7. Conclusion

Hajime Yoshino:


Hajime Yoshino:


Hajime Yoshino:


Hajime Yoshino:


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.

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I would like to conclude this lecture with most important

words:

Thank you!Danke schoene!

Hajime YOSHINO [email protected] http://www.meijigakuin.ac.jp/~yoshino

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