08 Milan Pres Um

7/31/2019 08 Milan Pres Um

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Presumption and Burden ofProof: IADA Workshop

Milan May 15-17 2008

Douglas Walton CRRAR

Centre for Research inReasoning, Argumentation &

Rhetoric: U. of Windsor


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BoP in Law and Everyday Argument

In law, what is called the normal default rule is thatthe party who makes the claim has the burden ofproof, but this rule is defeasible.

Under Roman law, the plaintiff had to make his casefirst (onus probandi), and the defendant could thenargue against it.

This same general principle, He who asserts must

prove, would appear to be applicable to everydayargumentation as well.


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Different Burdens of Proof in Law

Burden of Persuasion(also called legal burden ofproof): in a murder trial, the prosecution must prove

the charge that the defendant committed murder.

Evidential Burden(also called burden of production):if a person accused of burglary is found carrying

burglarious implements, an evidential burden is

placed on him to give some explanation of why he

had such articles in his possession. If he fails to do

so, the conclusion can be drawn he was carrying

them to commit burglary.


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Defining Burden of Persuasion

Burden of persuasion is set at the opening stage of a

persuasion dialog.

In contrast, presumptions and evidential burdens arebrought into play at the argumentation stage.

Burden of persuasion has three components: (a) a

contained proposition representing one arguers

thesis (ultimate probandum), (b) which arguer(proponent or respondent) has that thesis, and (c) a

standard of proof required for proving that thesis.


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First Example of a Presumption

Example: a son who wants to collect his fathers estate has aburden of persuasion to prove that his father is dead. There isno evidence of death, but the father has been absent for seven

years. However, this fact is not proof of death. In this case, the son can argue that he should collect the estate,on the grounds of a legal rule that raises a presumption.

LEGAL RULE: The proof that a person has disappeared fromhome and been absent for at least seven years, and nobody hasheard from this person during that period, raises a presumptionthat the person died during the seven years (McCormick onEvidence, Strong, 1992, 457).

Therefore, if the son can prove that the father has been absentfor at least seven years, that fulfills his burden of persuasion.


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Presumption of Innocence a Misnomer

Assignments of the burdens of proof prior to trial are notpresumptions. Before trial no evidence has been introducedfrom which other facts are to be inferred the assignment is made

on the basis of the rule of substantive law providing that oneparty or the other ought to have one or both of the burdens withregard to an issue.

In some instances, however, these substantive rules areincorrectly referred to as presumptions. The most glaringexample of this mislabeling is the presumption of innocence asthe phrase is used in criminal cases.

(Strong, McCormick on Evidence, 1992, 452)


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Burden of Proof and Presumption

It is often said that a presumption is a device that

shifts a burden of proof back and forth from one side

to the other in a dialog. However, presumption is one of the slipperiest

concepts in law, according to McCormick onEvidence(Strong, 1992, 449).

There are many different theories of presumption inargumentation studies from Whately onwards,

summarized in (Godden and Walton, 2007).


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Presumptive Reasoning

The Prakken-Sartor (2006) theory sees presumption

as equated with the rule that is part of a presumptive

inference.

However, the approach here defines presumption in

terms of the whole presumptive inference with three

components, one of which is the rule.

Thus the approach here sees presumption as being a

distinctive form of presumptive reasoning (plus

something else a dialog aspect).


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Reasoning and Argument

Reasoning is a process of inference in passing from

certain propositions assumed to be true (premises) to

other propositions in a sequence (Walton, 1990). Reasoning can be used for different purposes, for

example in explanations and arguments.

Argument, as contrasted with reasoning, will be

defined later (slide 29). There can be different kinds of reasoning.


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Deductive Reasoning

Premise: Luigi is an Italian soccer player.

Premise: All Italian soccer players are divers.

Conclusion: Luigi is a diver.

It is logically impossible for the premises to be

true and the conclusion false.

But is the first premise true?


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Inductive Reasoning

Premise: Luigi is an Italian soccer player.

Premise: Most Italian soccer players are

divers.

Conclusion: Probably Luigi is a diver.

It is improbable for the premises to be true

and the conclusion false.


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Defeasible Nonmonotonic Reasoning

Birds fly (defeasible generalization).

Tweety is a bird. Therefore Tweety flies

Exception: Tweety is a penguin.

Therefore Tweety does not fly.


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Deductive Inference as a Linked Argument


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Defeasible Inference: Tweety


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Inferential Structure of Presumptive Reasoning

PREMISE

Factual

Proposition

PREMISE

Generalization

(General Rule)

Argumentation

Scheme

CONCLUSION

(Presumption

Created)


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Strict Modus Ponens (SMP)

Major Premise: A => B Minor Premise: A

Conclusion: B


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Defeasible Modus Ponens (DMP)

Major Premise: A ~> B

Minor Premise: A

Conclusion: B


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Presumptive Inference Format


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Components of Presumptive Inference

There are three parts to the form of inference defining

a presumption (Ullman-Margalit, 1983, 147).

The first part is the presence of the presumption-

raising fact in a particular case at issue.

The second part is what she calls the presumption

formula, a defeasible rule that sanctions the passage

from the presumed fact to a conclusion.

The third part is the conclusion that is inferred: a

proposition presumed to be true on the basis of the

first two parts of the inference structure.


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Characteristics of a Fact

A fact corresponds to what in logic is called a simpleproposition, as contrasted with a rule, which takes aconditional form and therefore is classified in logic asa complex proposition.

The set of facts can be added to or deleted fromduring the argumentation stage. For example, a newfact can be introduced that is an exception to a rule.

A fact is a proposition that is accepted as true, bycriteria, even though it may later turn out to be false.

In law, the facts of a case consist of the evidencejudged to be admissible at the opening stage of atrial. A fact is a judicially admitted proposition.


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Characteristics of a Rule (Gordon, 2008)

1. Rules have properties, such as their date of enactment,jurisdiction and authority.

2. When the antecedent of the rule is satisfied by the facts of acase, the conclusion [consequent] of the rule is only presumablytrue, not necessarily true.

3. Rules are subject to exceptions. 4. Rules can conflict.

5. Some rule conflicts can be resolved using rules about rulepriorities, e.g. lex superior,which gives priority to the rule fromthe higher authority.

6. Exclusionary rules provide one way to undercut other rules. 7. Rules can be invalid or become invalid. Deleting invalid rules

is not an option when it is necessary to reason retroactively withrules which were valid at various times over a course of events.


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Rescher Form of Presumptive Inference

Premise 1: P(the proposition representing thepresumption) obtains whenever the condition C

obtains unless and until the standard default provisoD(to the effect that countervailing evidence is athand) obtains (Rule).

Premise 2: Condition Cobtains (Fact).

Premise 3: Proviso Ddoes not obtain (Exception). Conclusion: Pobtains. [2006, 33]


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The Burglar Tools Rule

Williams (1977, 156) offered the following example inEnglish law of a rule stated in section 25(3) of the

Theft Act: Where a person is charged with anoffence under this section, proof that he had with himany article made or adapted for use in committingburglary, theft or cheat shall be evidence that he hadit with him for such use. This rule relates to the

offense of possessing burglarious implements, asWilliams calls them.


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The Burglar Tools Inference


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The Dark Stairway Case

The plaintiff suffered a fall on a dark stairway in an

apartment building.

She sued the defendant, the buildings owner,claiming that he did not keep the stairway in a safe

condition, because the lighting did not work properly.

To prove notice, the plaintiff claimed she mailed a

letter to the defendant, informing him that several ofthe lights in the stairway no longer worked.


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The Mailed Letter Rule

RULE: A letter properly addressed, stamped, anddeposited in an appropriate receptacle is presumedto have been received in the ordinary course of the

mail (Park, Leonard and Goldberg, 1998, 103). Unless the presumption created by this rule is

rebutted, the properly addressed, stamped, anddeposited letter will be deemed to have beenreceived in what is considered to be the ordinary

amount of time needed in that delivery area (Park,Leonard and Goldberg, 1998, 103).


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The Mailed Letter Rule in an

Inference in the Stairway Case


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Inference and Presumption

An inference arises from premises that have

evidential weight, meaning they are factual and

supported by appropriate factual evidence.

A presumption arises from a rule that is established

for procedural and/or practical purposes in a type of

rule-governed dialog (like a trial).

In law, the distinction is drawn as follows: [An]

inference arises only from the probative force of theevidence, while the presumption arises from therule of law (Whinery, 2001, 554).


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What is an Argument?

An argument is an inference made up of premises and aconclusion, but is also an inference used for a conversationalpurpose to move ahead to fulfill a goal in a dialog (Walton 1990,p. 411). A dialog has two sides, the pro and the contra.

Each side has a burden of persuasion and a side wins if itsuccessfully discharges this burden by proving the propositionthat is its ultimate probandum.

Each single argument is put forward by one party to try to getthe other party to accept the conclusion of an inference that canbe used to move ahead toward in a chain of argumentation usedfor proving its ultimate probandum.


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Why Presumptions are Needed

The need for making a presumption arises during theargumentation stage when a particular argument is put forwardby one side.

A problem arises because there is some particular propositionthat needs to be accepted at least tentatively before theargumentation can move ahead, but at that point in the dialog,this proposition cannot be proved because the evidence that isavailable so far is insufficient.

The circumstances are such that collecting it would mean a

disruption of the dialog, because it would be too costly or taketoo much time to conduct an investigation to prove or disprovethis proposition by the standards required for properly acceptingor rejecting it.


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The Fair Trial as a Type of Dialog

This normative model of a fair trial is built around conceptsdrawn from semi-formal logic, where an argument has twolevels, an inferential level and a dialectical level.

At the inferential level, an argument is made up of the

inferences from premises to conclusions forming a chain ofreasoning. But such a chain of reasoning can be used fordifferent purposes in different types of dialog. When reasoning isused as argumentation in a in a dialog, it needs to be studied ata dialectical level.

There are different types of dialog, and each has itscharacteristic goals set at the opening stage. One type of dialogis a persuasion dialog, in which one party has the goal ofpersuading the other party to accept a particular propositioncalled its claim or thesis.


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The Burden of Persuasion

in the Stairway Example

The plaintiff sued the building owner, claiming he did

not keep the stairway in a safe condition.

In civil law, this claim needs to be proved on apreponderance of the evidence.

Her ultimate probandumwas the proposition that hedid not keep the stairway in a safe condition.

Hence the burden of persuasion was on her to provethat the stairway was unsafe.


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The Arguments on Both Sides

The argument the plaintiff gave to prove her claim

that the stairway was unsafe was that the lighting did

not work properly.

This argument would be defeated, however, if the

defendant had informed her beforehand that some of

the lights in the stairway no longer worked.

To defeat it, the defendant argued he had sent the

plaintiff a letter informing her that several of the lights

in the stairway no longer worked.


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The Plaintiffs Argument


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The

Defendants

Argument


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Problem #1: Presupposition

Whats the difference between a presumption and a

presupposition?

The king of France is bald [presupposition that thereis a King of France].

A presupposition is like a missing assumption that is

part of an assertion, and that was presumably

accepted by the hearer at some previous move in thedialog.


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Problem #2: Rebuttable Presumptions

In law, a distinction is often drawn between rebuttableand non-rebuttable presumptions.

In argumentation studies, it is often claimed thatsome presumptions are conclusive (non-rebuttable)while others are defeasible.

Wigmore and others, however, took the view that allpresumptions are rebuttable.

Are some presumptions conclusive, or are they allinherently defeasible?


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Problem #3:Rebuttal of Presumptions

How are presumptions rebutted?

There seem to be three different ways of attacking apresumptive inference?

You can (1) cast doubt on the facts, (2) attack therule, or (3) mount an opposed argument for theopposite of the proposition in the conclusion.

How does the distinction well known in AI betweenrebutters and undercutters apply? Is an undercutter

an argument that attacks the inference link, or merelyan argument attacking a rule?


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Problem #4: Commitment or Speech Act?

Is presumption a distinctive type of speech act in a

dialog that reverses the burden of proof in a dialog

(Walton, 1992 theory)?

Or is the presumption a kind of commitment that one

party in the dialog has to incur when the other side

makes the move of proposing that proposition as a

presumption (Krabbe, 2001 theory)?

Walton (speech act) theory versus the Krabbe

(commitment) theory.


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Problem #5:Lack of Evidence Inferences

What is the difference between a presumptive

inference and a lack of evidence inference (called

argumentum ad ignorantiamin logic)?

Premise: There are no known cases of Roman

military medals given posthumously.

Conclusion: The Romans did not give military medals

posthumously.

Implicit Premise: If there were cases of Roman

posthumous medals, we would know about them (by

evidence on gravestones etc.).


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References

David M. Godden and Douglas Walton, A Theory of Presumption for EverydayArgumentation, Pragmatics and Cognition, 15, 2007, 313-346.

Thomas F. Gordon, Hybrid Reasoning with Argumentation Schemes,Workshop on Computational Models of Natural Argument, ECAI, 2008.

Erik C. W. Krabbe, The Problem of Retraction in Critical Discussion, Synthese,127, 2001, 141-159.

Roger C. Park, David P. Leonard and Steven H. Goldberg, Evidence Law, St.

Paul, Minnesota, West Group, 1998. Henry Prakken and Giovanni Sartor, Presumptions and Burdens of Proof, Legal

Knowledge and Information Systems: JURIX 2006: The Nineteenth AnnualConference, ed. T. M. van Engers, Amsterdam IOS Press, 2006, 21-30.

Nicholas Rescher, Presumption and the Practices of Tentative Cognition,Cambridge, Cambridge University Press, 2006.

Leo Whinery, Presumptions and Their Effect Oklahoma Law Review, 54, 2001,553-571.

John William Strong, McCormick on Evidence, 4th ed., St Paul, Minnesota, WestPublishing Co., 1992.

Edna Ullman-Margalit, On Presumption, Jrnl. of Philosophy, 80, 1983, 143-163. Douglas Walton, Plausible Argument in Everyday Conversation, Albany, State

University of New York Press, 1992.

Glanville Williams, The Evidential Burden: Some Common Misapprehensions,New Law Journal, 153, 1977, 156-158.

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08 Milan Pres Um