Law Logic Summerschool 2012 Session 3.2.1 (Part 2): Burdens of proof and presumptions

1. Law Logic Summerschool 2012Session 3.2.1 (Part 2):Burdens of proof and presumptions Henry Prakken & Giovanni Sartor July 18, 2012

2. Burdens of proof (legally) • Burden of persuasion for P: who loses in the end if the evidence on P is balanced? • Burden of production for P: who loses on P if no evidence for P is provided during a proceeding? • Tactical burden: who would likely lose on P if the present stage were the final stage?

3. Dialectical status of arguments • Justified: survive conflict with all counterarguments • In in all labellings • Overruled: defeated by justified argument • Out in all labellings • Defensible: neither justified not overruled

4. Defining burden of proof (formally) • Burden of persuasion for P = task to have a justified argument for P in the final stage • Does not shift • Burden of production for P = task to construct a sensible argument for P during the initial stage at which P becomes relevant • Does not shift • Tactical burden on P: do something to make your favoured outcome on P likely if the resulting stage were the final stage • Can shift any number of times • Argumentation logic is applied to each stage in a proceeding

5. Burdens of proof:example Murder Prosecution has burden of persuasionfor Murder, Killing and Intent Killing Intent Rule 1 R1: If Killing & Intent then Murder R2:If Selfdefence then not R1

6. Burdens of proof:example Murder Prosecution has burden of persuasion for Murder, Killing and Intent Killing Intent Rule 1 Defence has tactical burdento do something, and burden of production for Selfdefence R1: If Killing & Intent then Murder R2:If Selfdefence then not R1

7. Burdens of proof:example Murder Exception to Rule 1 Prosecution has tactical burden to do something, and burden of persuasion against Selfdefence Killing Intent Rule 1 Selfdefence Rule 2 R1: If Killing & Intent then Murder R2:If Selfdefence then not R1

8. Burdens of proof:example Murder Exception to Rule 1 Prosecution has burden of persuasion against Selfdefence Kill Intent Rule 1 Selfdefence Rule 2 No selfdefence

9. Burdens of proof:example Proof standard captured in bandwith for mutual defeat Murder Exception to Rule 1 Prosecution has burden of persuasion against Selfdefence so must strictly defeat Kill Intent Rule 1 Selfdefence Rule 2 No selfdefence

10. Presumptions: not used to allocate but to fulfill burden of proof R1: IfDamaged & Owner then Compensation Possession creates a legal presumption for ownership

11. Presumptions:they are defeasible conditionals Compensation R1: If Damaged & Owner then Compensation R2: If Possession then Owner Damaged R1 Owner e1 R2 Possession e2

12. Their antecedent must be proven Compensation R1: If Damaged & Owner then Compensation R2: If Possession then Owner Damaged R1 Owner e1 R2 Possession No Possession e2 e3

13. Compensation R1: If Damaged & Owner then Compensation R2: If Possession then Owner Damaged R1 Owner e1 R2 Possession No Possession e2 e3

14. They cannot be used after counterevidence Compensation R1: If Damaged & Owner then Compensation R2: If Possession then Owner R3: If e4then R2 does not apply Damaged R1 Owner Not Owner e1 R2 Possession n.a.R2 e2 R3: e4

15. Now real evidence is needed Compensation Damaged R1 Owner Not Owner e1 e5 e4

16. Summary • Various notions of burdens and standards of proof can be defined in terms of defeasible argumentation • But dynamic setting is needed • Presumptions can be logically understood as defeasible conditionals • Not used to allocate but to fulfill proof burdens