Transcript Need for Logic of Argumentation

KNOWLEDGE AND ACTION IN
RATIONAL DELIBERATION
Douglas Walton
CRRAR
7th Conference on Analytic Philosophy
in China, Shanghai, Oct. 30, 2011
Bounded Procedural Rationality
• In this paper it is shown how knowledge can lead to a
rational decision for action or inaction based on
argumentation process called deliberation.
• The viewpoint adopted is one of bounded procedural
rationality based on a notion of defeasible knowledge.
• The problem confronted is that decision-making about
real-world problems needs to be made under
conditions of uncertainty, and even apparent
inconsistency where there is both pro and contra
evidence for a conclusion to be decided.
Argumentation Methods
• It is just in this kind of case that methods of
argumentation are especially useful.
• Argumentation can be defined as a procedure to
identify, analyze and evaluate the arguments on both
sides of a claim, and to use the evidence that is
collected by this procedure to determine whether to
accept the claim or not.
• It is also a part of argumentation methodology that
setting a burden of proof on each side by determining
what kind of arguments are relevant, and what
standards of proof should be required, is an essential
requirements of the procedure.
First Example
• Let’s consider the case of the student who is writing an
essay. He is collecting all kinds of knowledge from books
and periodicals, but he has a strict deadline for finishing the
assignment.
• This problem is to determine when he should stop
searching for new knowledge and attempt to write the
essay. The longer he delays writing in order to search for
new knowledge, the better the essay will be. But if he
delays too long, he will not have enough time to properly
write the essay, and the result will be that the essay will not
be very good.
• The general problem in many comparable cases of this kind
is one of when to terminate the process of deliberation and
close off the collecting of new knowledge.
Second Example
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Another kind of example can also be cited. In July 2010, scientists found a
way of altering the DNA of mosquitoes that shortens their lifespan so that
malarial parasites to not have enough time to grow to maturity. This
discovery gives the scientists the possibility of releasing a malaria-proof
mosquito into the wild, thereby eliminating mosquitoes that can cause
malaria. Right now malaria kills about one million people every year.
However, there is a problem. Altering the DNA of mosquitoes might make
them better carriers of other diseases.
This proposal cannot be carried out for another ten years, and even then,
there may be no way to know what the consequences are.
Once the malaria-proof mosquito is produced by the scientists, even
though we can study the problem and collect knowledge about it, we will
never know what all the side-effects will be until we release the new
mosquitoes into the wild.
R. M. Schneidermann, ‘God lives in a Lab in Arizona’, Newsweek, August 9,
2010, 8.
Aquinas Poses the Problem
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Aquinas asked the question, “May deliberation go on endlessly?” and
answered it in his Summa Theologiae in Question 14, Article 6; quoted
from (Blackfriars Edition, 155):
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• 1. Yes, apparently, for it is about the particular things which are the
concern of practical knowledge. These are infinite. Accordingly no term is
to be set to the inquiry of deliberation about them.
• 2. Further, we have to weigh up not only what has to be done, but also
how to clear away the obstacles. Now any number of objections to any
particular course of action can be put up and knocked down in our mind.
Therefore there is no stop to our questioning about how to deal with
them.
• 3. Moreover, the inquiry instituted by demonstrative science does not lead
back indefinitely, but arrives at self-evident principles which are altogether
certain. Such certainty, however, cannot be found in contingent and
individual facts, which are variable and uncertain. Deliberation, therefore,
goes on endlessly.
The Closed World Assumption
• The closed world assumption is the inference drawn that
any positive fact not specified in a given database may be
assumed to be false, on the basis that all of the relevant
knowledge has been specified (Reiter, 1987).
• Consider the familiar example (Reiter 1980, 69) of scanning
an airline monitor. Let’s say that no direct flight is listed
from Windsor to Shanghai. The closed world assumption is
that all the relevant data on flights leaving from Windsor at
this time are listed on the monitor on the airport website.
• So if a direct Windsor to Shanghai flight is not listed, it is
reasonable to draw the conclusion that no such flight is
available. In this situation, the closed world assumption is
reasonable to invoke, because we have good reason to
assume that the knowledge base is complete.
Another Example
• The official listing of baseball statistics about hits,
home runs and so forth, is known to not only be
complete for the major-league baseball teams, but also
highly reliable, because there are many fans who are
passionate about keeping baseball statistics, and who
would immediately challenge any error they might find
in the baseball statistics knowledge base.
• So if we were to look in the database and see that
some information about some home runs alleged to be
hit in 1936 was not in it, we could very confidently
invoke the closed world assumption to draw the
conclusion that there were no such home runs hit that
year.
Scheme for Practical Reasoning
• Major Premise: I have a goal G.
• Minor Premise: Carrying out action A is a means to
realize G.
• Conclusion: I ought (practically speaking) to carry out
action A.
• The first-person singular pronoun ‘I’ in the scheme for
practical reasoning above represents an agent. An
agent is an entity that has goals and knowledge about
its circumstances, can take action in its circumstances
based on this knowledge, and can also see the
consequences of its actions so that it can correct them
through feedback.
Critical Questions Matching Scheme
• CQ1: What other goals do I have that should be
considered that might conflict with G?
• CQ2: What alternative actions to my bringing about A
that would also bring about G should be considered?
• CQ3: Among bringing about A and these alternative
actions, which is arguably the most efficient?
• CQ4: What grounds are there for arguing that it is
practically possible for me to bring about A?
• CQ5: What consequences of my bringing about A
should also be taken into account?
How to Use Critical Questions
• These five basic critical questions for practical
reasoning are not complete.
• As shown in (Walton 1990), each of these five
critical questions has critical sub-questions.
• The five basic critical questions are meant as
devices to help a critic or student of critical
thinking find weak points in an argument of
this type that can be challenged or cast into
doubt.
Value-based Practical Reasoning
• Value-based practical reasoning (Atkinson, Bench-Capon and
McBurney, 2006) is made up of two more basic schemes, the one
for practical reasoning and the one for argument from values
(Bench-Capon, 2003). The argumentation scheme for value-based
practical reasoning has this form (Atkinson, Bench-Capon and
McBurney, 2006).
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• Scheme for Value-based Practical Reasoning
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In the current circumstances R
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we should perform action A
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to achieve New Circumstances S
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which will realize some goal G
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which will promote some value V.
Questioning versus Arguing
• Asking the critical question C5 needs to be backed up
with some evidence of what the negative
consequences are before an argument based on
practical reasoning is refuted.
• When this happens, the asking of this critical question
can also be analyzed as a counter-argument.
• Argument from negative consequences cites the
consequences of a proposed course of action as a
reason against taking that course of action.
• This argument also has a positive form in which
positive consequences of an action are cited as a
reason for carrying out the action.
Argument from Consequences
• Scheme for Argument from Positive Consequences
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• Major Premise: Its having good consequences is a reason for doing
something.
• Minor Premise: If A is brought about, good consequences will plausibly
occur.
• Conclusion: A should be brought about.
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• Scheme for Argument from Negative Consequences
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• Major Premise: Its having good consequences is a reason for not doing
something.
• Minor Premise: If A is brought about, then bad consequences will occur.
• Conclusion: A should not be brought about.
The Carneades System
• The Carneades Argumentation System uses
argumentation schemes and critical questions for
argument analysis and evaluation (Gordon, 2010).
• Carneades is a computational model consisting of
mathematical structures and functions on them
(Gordon, Prakken and Walton, 2007).
• Carneades models the structure of arguments, the
acceptability of statements, and burdens of proof.
• Carneades has an open source graphical user interface
(http://carneades.github.com/ ).
Tweety Example
Wiki Example 1
Problem with Critical Questions
• It would be very nice if the five critical questions for
practical reasoning could be represented as additional
premises of the argumentation scheme. Then we could
represent the critical questions as implicit assumptions
of the argument when we analyze the argument using
an argument diagram of the standard kind.
• However, there is a problem. With some critical
questions, simply asking the question is enough to
defeat the original argument, whereas with other
critical questions, merely asking the critical question is
not enough to defeat the argument. In order to defeat
the argument some evidence has to be given to back
up the critical question.
Solution to the Problem
• To solve this problem, the Carneades system offers two
ways of responding the asking of a critical question by
distinguishing three types of premises in argumentation
scheme, called ordinary premises, assumptions and
exceptions (Walton and Gordon, 2009).
• Ordinary premises are explicitly stated premises of the
argumentation scheme. They are assumed to hold
tentatively, but if challenged they may have to be given up.
• Assumptions, like ordinary premises, are assumed to be
true.
• Exceptions are assumed not to hold, and therefore they do
not defeat an argument unless backed up by evidence to
support them.
Carneades Map of Practical Reasoning
Evaluating Arguments
• Based on this method of representing the critical questions of an
argumentation scheme by representing them as different kinds of
premises of scheme, Carneades has a computational method for
evaluating arguments (Gordon and Walton, 2006).
• At each stage of the argumentation process, an effective method
(decision procedure) is used for testing whether the conclusion of
an argument is acceptable or not, given knowledge about whether
its premises are acceptable or not.
• The assumptions represent undisputed facts, the current consensus
of the participants, or the commitments or beliefs of some agent,
depending on the task.
• The evaluation of the given argument may depend on the proof
standard applicable to the proposition at issue, and on the dialogue
procedure the argument is embedded in.
Dialogue Models
• Dialogue models have rules on how participants should
ideally speak and respond in order to achieve a
common conversational goal.
• Dialogue models of argumentation (Walton and
Krabbe, 1995) have proved their usefulness in
argumentation studies, artificial intelligence, and multiagent systems (Bench-Capon, 2003; Prakken, 2005).
• Walton and Krabbe (1995) identified six primary types
of dialogue: information-seeking dialogue, inquiry,
deliberation, persuasion dialogue, negotiation and
eristic (quarrelsome) dialogue.
Formal Dialogue Systems
• A dialogue is generally a group activity with multiple
participants, but in the simplest case there are only two
parties called the proponent and the respondent.
• A dialogue is defined in the Carneades model as an ordered
3-tuple <O, A, C> where O is the opening stage, A is the
argumentation stage, and C is the closing stage (Gordon
and Walton, 2009, 5).
• Dialogue protocols regulate the types of moves that are
allowed and how a participant must respond to a previous
move made by the other party (Walton and Krabbe, 1995).
• So far, Carneades has not provided protocols for
deliberation dialogues, but there is a formal model.
Deliberation Dialogue
• The initial situation of deliberation is the need for action arising out of a
choice between alternative competing courses of action.
• The collective goal of this type of dialogue is for the participants to
collectively decide on what is the best available proposal for action that
has been put forward for the group at the proposal stage, once that stage
has been reached.
• Once that stage has been reached, the participants evaluate the proposals
in a process in which each party puts forward its own proposals and
critically evaluates the competing proposals put forward by others.
• There is also a prior ‘inform’ stage where the facts collected and shared
among the participants.
• In a successful deliberation, the strengths and weaknesses of each
proposal are brought out by the discussion, and this evidence is used to
judge which proposal is the one that should be selected to move forward
with.
8 Stages of Deliberation Dialogue
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Open: In this stage a governing question is raised about what is to be done. A
governing question, like ‘Where shall we go for dinner this evening?’ is posed.
Inform: This stage includes discussion of desirable goals, values, constraints on
possible actions, evaluation criteria for proposals, and determination of relevant
facts.
Propose: Proposals cite possible action-options relevant to the governing question
Consider: This stage concerns commenting on the proposals from various
perspectives.
Revise: Goals, constraints, perspectives, and action-options are revised in light of
comments presented and information gathering as well as fact-checking.
Recommend: A proposal for action is recommended for acceptance or nonacceptance by each participant.
Confirm: The participants can confirm acceptance of the recommended proposal
according to some procedure they have agreed on.
Close: The termination of the dialogue takes place.
(Hitchcock, McBurney and Parsons, 2007)
Judging a Deliberation Dialogue
Scientific Inquiry and Truth
• According to the traditional view the conclusion of an inquiry has to
be drawn by the deductive chain of reasoning from a set of
premises that are absolutely certain.
• Any scientific inquiry might lead to a conclusion which might need
to be revised in the future (Peirce, 1931, 2.75). Popper called this
falsifiability.
• Peirce wrote that many things are “substantially certain” (Peirce
1931, 1.152), but that this is different from the kind of absolute
certainty that implies truth.
• On his view truth is an important motivation for scientists to have
as the ultimate goal of scientific research, but he argued that that
truth can only be arrived at beyond all doubt by an inquiry that
would take an infinite amount of time.
Fallibilism of Peirce and Popper
• On their view, knowledge does not imply truth. In
other words, it is not a requirement for
proposition to be part of knowledge that it be
true, at least in any sense requiring that it will not
turn out to be false in the future.
• On this view, called fallibilism, scientific
knowledge is defeasible, meaning that even
though a proposition is accepted as knowledge, it
might be defeated in the future by enough
evidence casting doubt on it, or even showing
that it is false, so that it needs to be retracted.
Defeasible Knowledge
• Peirce described the process of inquiry as one in which different
participants set out with conflicting views, but are led through a
process of marshalling and testing evidence to accepting the same
conclusion. This convergence takes place as a successful inquiry
moves to completion.
• According to (Walton, 2010) Peircean belief is characterized as a
settled state we do not wish to change. Once fixed, it is something
we cling tenaciously to. It is an indication of a habit, and a matter of
degree.
• It puts us into a condition so we act in a certain way in the future,
and it guides our desires and shapes our actions.
• On this view, defeasible knowledge is a species of belief that is fixed
firmly by a scientific discipline through process of inquiry that tests
the belief as a hypothesis against all the pro and contra evidence
that can be collected and is relevant to proving or disproving it.
Proof Standards
• The following four standards of proof are used in the Carneades
Argumentation System (Gordon and Walton, 2009).
• Scintilla of Evidence (SE) is met if there is at least one applicable argument
for a claim.
• Preponderance of the Evidence (PE) is met if SE is satisfied and the
maximum weight assigned to an applicable pro argument (for the claim) is
greater than the maximum weight of an applicable con argument (against
the claim).
• Clear and Convincing Evidence (CCE), is met if PE is satisfied, the maximum
weight of applicable pro arguments exceeds some threshold α, and the
difference between the maximum weight of the applicable pro arguments
and the maximum weight of the applicable con arguments exceeds some
threshold β.
• Beyond Reasonable Doubt (BRD) is met if CCE is satisfied and the
maximum weight of the applicable con arguments is less than some
threshold γ.
The Mosquitoes Example
• The collection of knowledge phase will only be reached
at some point after ten years. At this point there will
have to be deliberations that many organizations will
take part in, including the World Health Organization,
which will need to develop rules for testing genetically
modified mosquitoes.
• However, even at this point, it is possible to see how
the argumentation structure of the deliberation in this
case takes a pro and contra argument form based on
argumentation schemes.
Carneades Map of Mosquitoes
Argumentation
Evaluation of Mosquitoes Case
• This method of moving forward with an evaluating deliberation
requires taking fully into account evidence obtained from scientific
inquiry into the circumstances of the case.
• On this model, the factual basis of evidence from the scientific
inquiry is part of what is required to assess the depth of assessment
of the proposals made in the deliberation dialogue.
• The dialogue should only be closed when this depth of assessment
by argumentation has met the standard of evidence set for this
deliberation dialogue.
• At some point the cost in lives due to malaria will require that the
decision be made one way or the other, provided that the
alternative of doing nothing continues to result in highly significant
loss of human lives.
Conclusion
• The paper has shown how a rational decision on what to do
depends on an evaluation of the pro and contra arguments
for each proposal, once all the proposals have been stated.
• It has also shown that this decision depends on how well
informed these proposals are, based on the scientific and
factual evidence concerning the circumstances of the case.
• To provide a method for making these decisions, the paper
has utilized formal dialectical models of deliberation
dialogue and inquiry dialogue, showing how the latter type
of dialogue is embedded in the former.
3 Problems for Further Research
• The first is to devise computational argumentation
tools to measure the depth of argumentation behind a
proposal that has been discussed in a deliberation
dialogue by the closing stage.
• The second is to show how knowledge is transferred
from inquiry dialogue to deliberation dialogue,
typically using the argumentation scheme for argument
from expert opinion.
• The third is to apply the methods of this paper to a
more detailed example of deliberation using
knowledge obtained from scientific inquiry.
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