The Structure of Argumentative Legal Texts

Transcription

1 The Structure of Argumentative Legal Texts Henry Prakken LEX Summerschool Fiesole,

2 Overview Why does legal reasoning involve argumentation? The general structure of arguments Arguments and counterarguments Argument schemes + critical questions Marking up arguments in legal texts

3 Part 1: Why does legal reasoning involve argumentation?

4 What is argumentation? Giving reasons to support or criticise claims that are open to doubt logic + dialectic Often to persuade someone else rhetoric Proponent: Opponent: Proponent: Opponent: Proponent: Regarding downloading Mp3s as copying for private use is wrong Why? Because it makes normal commercial exploitation of music impossible Why? Because it s so easy to copy, upload and download MP3s

5 What is argumentation? Giving reasons to support or criticise claims that are open to doubt logic + dialectic Often to persuade someone else rhetoric Proponent: Opponent: Proponent: Opponent: Proponent: Opponent: Proponent: Opponent: Regarding downloading Mp3s as copying for private use is wrong Why? Because it makes normal commercial exploitation of music impossible Why? Because it s so easy to copy, upload and download MP3s But there are quite profitable ways to sell Mp3s online Really? Look at itunes

6 Legal contexts of argumentation In court In public administration In consultancy In scholarly debate In parliamentary debate In public debate

7 Legal reasoning: three stages Determining the facts of the case Classifying the facts under the conditions of a legal rule Applying the rule

8 Legal reasoning is considering arguments pro and con Determining the facts of the case Uncertainty, conflicting sources of evidence Classifying the facts under the conditions of a legal rule Vagueness of legal language Applying the rule Conflicting rules Reasons not to apply the rule

9 Evidence problems General terms Exceptions Purpose of the rule Principle Example Vehicles are not allowed in the park

10 Legal reasoning is adversarial Legal cases involve clashes of interest Dispute study constructing and attacking arguments

11 Part 2: The structure of legal arguments

12 The structure of arguments: basic elements Arguments have: Premises A conclusion Ways to get from premises to conclusion Applications of argument schemes Conclusion Licenced by some argument scheme Premise 1.. Premise n

13 Two types of support Cumulative (all premises needed for conclusion) Minor Person < 18 Alternative (one premise suffices for conclusion) Written offer Offer in letter Offer in

14 Third type of support? Minor Cumulative (all premises needed for conclusion) Person < 18 Written offer Alternative (one premise suffices for conclusion) Offer in letter Offer in S was at crime scene Aggregate (the more support the better) S s DNA matches DNA found at crime scene Witness W saw S at crime scene

15 + Combined types of support Cumulative + alternative Written offer Offer in letter Offer in IF Offer in letter OR offer in THEN offer in writing

16 Contract A-B A offered B accepted B requested offer A replied will supply B: I accept B: will you supply? Document 2 Document 3 Document 1

17 Contract A-B A offered An offer and an acceptance create a contract B accepted B requested offer A replied will supply B: I accept B: will you supply? Document 2 Document 3 Document 1

18 Contract A-B A offered An offer and an acceptance create a contract B accepted B requested offer R2 A replied will supply B: I accept B: will you supply? A reply will supply.. in response to a request for offer is an offer Document 2 Document 3 Document 1

19 Contract A-B A offered An offer and an acceptance create a contract B accepted B requested offer R2 A replied will supply B: I accept B: will you supply? R3 Document 2 Document 3 Document 1 A statement will you supply..? is a request for offer

20 Contract A-B A offered An offer and an acceptance create a contract B accepted B requested offer R2 A replied will supply R4 B: I accept B: will you supply? R3 Document 2 A statement I accept.. is an acceptance Document 3 Document 1

21 Contract A-B A offered An offer and an acceptance create a contract B accepted B requested offer R2 A replied will supply R4 B: I accept B: will you supply? R3 Document 2 R5 Document 3 Document 1 Documents of this type are reliable evidence of their content

22 Arguments and counterarguments

23 The structure of arguments: basic attacks Arguments have: Premises A conclusion Ways to get from premises to conclusion Applications of argument schemes So arguments can be attacked on: Their premises Their conclusion The connection between premises and conclusion

24 Two types of counterarguments: rebuttals and undercutters smoking increases the chance of cancer Expert E1 says that smoking increases the chance of cancer Experts are usually right

25 Two types of counterarguments: rebuttals and undercutters smoking increases the chance of cancer smoking does not increase the chance of cancer Expert E1 says that smoking increases the chance of cancer Experts are usually right Expert E2 says that smoking does not increase the chance of cancer Experts are usually right

26 Two types of counterarguments: rebuttals and undercutters smoking increases the chance of cancer smoking does not increase the chance of cancer Expert E1 says that smoking increases the chance of cancer Experts are usually right Expert E2 says that smoking does not increase the chance of cancer Experts are usually right Expert E2 is biased Expert E2 is payed by a tobacco company Experts usually are biased toward who pays them

27 Murder Killing Intent R1

28 Murder Killing Intent R1 Exception to R1 Selfdefence R2 Threat to life Killing R3 R4 Knife W1 says knife

29 Murder Killing Intent R1 Exception to R1 Selfdefence R2 No threat to life Threat to life Killing R3 Time to run away R5 R4 Knife W2 says time to run away W1 says knife

30 Murder Killing Intent R1 Exception to R1 Selfdefence R2 No threat to life Threat to life Killing R3 Time to run away R5 R4 Knife W2 says time to run away W1 says knife

31 Murder Killing Intent R1 Exception to R1 Selfdefence R2 No threat to life Threat to life Killing R3 Time to run away R5 R4 Knife W2 is biased W2 says time to run away W2 is friend of victim R6 W1 says knife

32 Part 4: Adjudicating conflicts between arguments

33 Justifying your argument: refute every attack Argument for claim

34 Dialectical status: an argument game Argument for claim argument 1 argument 2

35 Dialectical status: an argument game Argument for claim argument 1 argument 2 argument 1.1 argument 2.1

36 Dialectical status: an argument game Argument for claim argument 1 argument 2 argument 1.1 argument 2.1 argument argument 2.1.2

37 Dialectical status: an argument game Argument for claim argument 1 argument 2 argument 1.1 argument 2.1 argument argument argument argument

38 Murder Killing Intent R1 argument 1 argument 2 argument 1.1 argument 2.1 argument argument argument argument

39 Murder Exception to R1 Killing Intent R1 Selfdefence R2 Threat to life Killing R3 argument 1 R3 Knife W1 says knife argument 1.1 argument 2.1 argument argument argument argument

40 Part 5: Argument schemes and critical questions

41 Argument schemes: general form Many arguments (and attacks) follow patterns Premises of certain types A conclusion of a certain type But also critical questions Negative answers are counterarguments

42 Legal rule application (simplistic) IF conditions THEN legal consequence conditions THEREFORE, legal consequence

43 Legal rule application: critical questions Is the rule valid? Is the rule applicable to this case? Must the rule be applied? Is there a statutory exception? Does applying the rule violate its purpose? Does applying the rule have bad consequences? Is there a precedent in which the rule was not applied?

44 Witness testimony Critical questions: Is W sincere? Witness W says P Therefore (presumably), P Does W s memory function properly? Did W s senses function properly?

45 Expert testimony E is expert on D E says that P P is within D Therefore (presumably), P is the case Critical questions: Is E biased? Is P consistent with what other experts say? Is P consistent with known evidence?

46 Arguments from consequences Action A brings about G, G is good (bad) THEREFORE, A should (not) be done Critical questions: Does A also have bad (good) consequences? Are there other ways to bring about G?...

47 Example Making spam a criminal offence is good Making spam a criminal offence is bad Making spam a criminal offence reduces spam Reduction of spam is good Making spam a criminal offence increases workload of police and judiciary Increased workload of police and judiciary is bad

48 Example Making spam a criminal offence is good Making spam a criminal offence is bad Making spam a criminal offence reduces spam Reduction of spam is good Making spam a criminal offence increases workload of police and judiciary Increased workload of police and judiciary is bad Civil liability for spam reduces spam

49 Part 6: Marking up arguments in legal texts

50 Argumentation in legal knowledge-based systems No practical applications yet Overview: Bench-Capon & Prakken (2006) Case-based argumentation Rule-based argumentation Combining case-based and rule-based argumentation Systems based on argument schemes

51 Argumentation management systems Support for drafting and visualising argumentation structuring argumentative texts Useful for: Sense making Case file management Not knowledge-based!

52 Marking up arguments in legal texts: some issues (1) What are reliable linguistic indicators of: Structural elements of arguments? (elements of) argument schemes? Critical questions? Could automated text mining be of help?

53 Marking up arguments in legal texts: some issues (2) Implicitness Legal background knowledge Conditional generalisations Contract Defendant and I have a contract because I made an offer and she accepted The accused showed consciousness of guilt since he fled from the crime scene when the police arrived Offer Acceptance IF Offer AND Acceptance THEN Contract

54 Marking up arguments in legal Ambiguity texts: some issues (3) Cumulative, alternative or aggregate premises? The accused was at the crime scene since his DNA matches DNA found at the scene and witness W saw him there

55 Marking up arguments in legal texts: some issues (3) Size

56 Conclusion Legal reasoning is (almost) never conclusive Uncertainty Disagreement Conflicts of interest Legal reasoning therefore is argumentation AI (& Law) has computational models of (legal) argumentation available Knowledge-based applications not yet realistic But argumentation management systems are feasible

57 Further reading H. Prakken, Legal Argumentation. Lecture notes University of Groningen, T.J.M. Bench-Capon & H. Prakken, Argumentation. (Chapter in Lodder & Oskamp, 2006) M. Lauritsen, Intelligent tools for managing factual arguments (ICAIL-2005), J. Sombekke, T.M. Van Engers & H. Prakken, Argumentation structures in legal dossiers (ICAIL- 2007)