Transcript Slide 1

A Dialectical Model of Scientific
Discovery and Inquiry
University of Groningen Lecture Sept. 29, 2011
Douglas Walton
Centre for Reasoning and Argumentation
University of Windsor, Ontario
8 PARTS: First Four Parts
• In the first part, a case study of scientific discovery of
the cause of pernicious anemia is presented.
• In the second part, an argumentation scheme for
argument from correlation to causation is introduced
• In the third part, formal models of dialogue of the kind
used to analyze argumentation are explained.
• In the fourth part, the properties of a type of dialogue
called the inquiry are explained.
Last Four Parts
• In the fifth part, a type of dialogue called
discovery dialogue is introduced.
• In the sixth part, the transition from the
discovery phase to the later proof phase is
modeled as a dialectical shift.
• In the seventh part, it is shown on the notion of
burden of proof is essential for inquiry.
• The conclusions are in the eighth part.
• In 1923 George R. Minot and William P. Murphy
sought a cure for pernicious anemia, a disease
characterized by low counts of red blood cells.
• George Whipple had earlier found that the best
treatment for anemic dogs was to feed them
liver.
• Minot and Murphy tested this treatment on
human patients, and found that it worked.
• They shared the Nobel Prize in 1934.
The Cure Worked but the Cause
Was not Known
• Dr. William Castle noted that people with their
stomachs removed often died because of anemia, and
was led by a series of experiments to formulate the
hypothesis that something in the stomach was related
to the disease.
• As an experiment, he ate red meat, forced himself to
vomit, and then had patients eat his regurgitated
stomach contents.
• This revolting experiment led to scientific inquiry that
proved that the substance necessary for red blood cell
formation (found abundantly in liver) was vitamin B12.
Whipple, Minot and Murphy
Sequence of Argumentation in the
Anemia Example
(Walton, 2004) Abductive
Reasoning Argumentation Scheme
• F is a finding or given set of facts.
• E is a satisfactory explanation of F.
• No alternative explanation E’ given so far is as
satisfactory as E.
• ___________________________________
• E is plausible, as a hypothesis.
Critical Questions (Walton, 2004)
• CQ1: How satisfactory is E itself as an
explanation of F, apart from the alternative
explanations available so far in the dialogue?
• CQ2: How much better an explanation is E than
the alternative explanations available so far?
• CQ3: How far has the dialogue progressed? How
thorough has the search been in the inquiry?
• CQ4: Would it be better to continue the
dialogue, instead of drawing a conclusion?
Scheme for Argument from
Correlation to Causation
• There is a positive correlation between A
and B.
• Therefore A causes B.
• Evaluating causal argument is best carried in a
dialogue format using critical questions.
Three Critical Questions
• Is there good evidence that the causal
relationship goes from A to B, and not just from
B to A?
• Can it be ruled out that the correlation is
accounted for by some intervening factor?
• Can it be shown that the increase or change in B
is not solely due to the way B is defined, or the
way entities are classified?
The Causal Relation
• The causal relation is controversial to define,
but it means something roughly like this.
• A is one of a set of conditions that are (when
taken together) sufficient for the occurrence of
B, and A is also a necessary condition for the
occurrence of B.
• Also, A must meet some pragmatic
requirements.
Inquiry
• The goal of the inquiry is to prove that a
statement designated at the opening stage as
the probandum is true or false, or if neither of
these findings can be proved, to prove that
there is insufficient evidence to prove that the
probandum is true or false.
• The most important characteristic of the inquiry
as a type of dialogue is the property of
cumulativeness
A Case of Retraction in Inquiry
• Astronomer Andrew Lyne observed a pattern of periodically
blinking stars, and concluded that this observation could only be
explained by the postulation of the existence of a previously
undiscovered planet (Walton, 1998, 71).
• After he re-examined his original analysis of the data, he
concluded that it contained two small measurement errors that
provided sufficient grounds for retracting his earlier hypothesis.
• It was an emotional moment when he had to admit his error at a
scientific meeting. Initially the audience felt pity for him, but at
the end of his talk the audience applauded, evidently
acknowledging his honesty and courage that must have
motivated such an admission.
Cumulative Argumentation in the
Kripke Model
C. S. Peirce on Inquiry
• Peirce advocated a fallibilism that admits of the
susceptibility of scientific proof to error.
• On his view, even the most careful scientific
inquiry might produce an outcome which could
later be shown to be wrong (Peirce, 1931, 2.75).
• Peirce wrote that many things are
“substantially certain” (Peirce 1931, 1.152), but
that this is different from absolute certainty.
Peirce on Truth and Inquiry
• On his view truth is an aim of inquiry, and an
important motive for scientific research, but to
arrived at truth beyond all doubt would take an
infinite amount of time.
• It was part of his view that the fixing belief by
“tenacity” or “authority” blocks inquiry by
implying claim that no further inquiry is
necessary (Cooke, 2006, 34).
Popper on Inquiry
• The procedure of inquiry was seen by Popper
(1962, 312) as a continuous movement of trial
and error that proceeds by degrees of
improvement, and that can reach an outcome
that is provisionally acceptable.
• On his theory, even though a theory or
hypothesis can be accepted as part of science, it
must always remain open to falsification.
Bounded Procedural Rationality
• Popper held that scientific inquiry is based on an
evidential procedure that moves toward truth
and is independent of the knowing subject.
• Both Peirce and Popper viewed the inquiry as a
procedure that uses evidence pro and con a
hypothesis to move forward to tentative
acceptance of a scientific theory or
experimental finding, but is open to retraction.
• According to the sequence of argumentation
shown in the next figure, a standard of proof
needs to be set at the opening stage.
• During the argumentation stage, evidence for
and against the proposition is brought forward.
• As determined by the availability of time and
resources, the sequence of argumentation must
eventually be closed off.
Evidence and Standards of Proof
Employed in an Inquiry
Discovery Dialogue
• Discovery dialogue (McBurney and Parsons, 2001, 5) moves through ten
stages (McBurney and Parsons, 2001, 5) called open dialogue, discuss
purpose, share knowledge, discuss mechanisms, infer consequences, discuss
criteria, assess consequences, discuss tests, propose conclusions, and close
dialogue.
• The participants open the discussion, share knowledge by presenting data
items to each other, build arguments by inferring consequences from data
items, discuss criteria for assessment of consequences presented, assess the
consequences in light of the criteria, pose one or more conclusions for
possible acceptance, and close the dialogue.
• The stages of the discovery dialogue may be undertaken in any order and
may be repeated (2001, 6).
• However, they don’t at least directly consider how their model might be
applied to scientific discovery
Dialogue Model for Scientific
Discovery
Burden of Proof
• The burden of proof at the closing stage in a
discovery dialogue is different from the way
burden of proof works in an inquiry dialogue.
• In an inquiry, the aim is to avoid retraction
insofar as this is possible, and therefore a high
standard of proof needs to be set.
• The conclusion accepted in a discovery dialogue
is much more and conjectural nature.
BoP in Discovery Dialogue
• A hypothesis may be tentatively accepted even though
the evidence supporting it is slight, provided there is no
evidence against it, and there is no competing
hypothesis more strongly supported by the evidence.
• The aim of a discovery dialogue is not to prove
something to a high standard, but only to provide a
hypothesis that enables an investigation to move
forward by collecting more evidence that will be useful
in an inquiry dialogue, once the evidence that has been
amassed is sufficient to justify opening an inquiry.
Dialectical Shifts
• A dialectical shift occurs in cases where, during a sequence of argumentation,
the participants begin to engage in a different type of dialogue from the one
they were initially engaged in (Walton and Krabbe, 1995).
• In the following classic case often cited as an example, two agents are
engaged in deliberation dialogue on how to hang a picture.
• Engaging in practical reasoning they come to the conclusion they need a
hammer, and a nail, because they have figured out that the best way to hang
the picture is on a nail, and the best way to put a nail in the wall is by means
of a hammer. One knows where a hammer can be found, and the other has a
pretty good idea of where to get a nail.
• At that point, the two begins to negotiate on who will get the hammer and
who will go in search of a nail. In this kind of case, we say that the one
dialogue is embedded in the other (Walton and Krabbe, 1995),
We Can Use Argument Mapping
Tools like Rationale
The Carneades Argumentation
System
• Gordon and Walton (2009) have defined an abstract formal
model of argumentation called Carneades that works as a theory
and proof construction process for making justified decisions
that can be applied to scientific as well as legal argumentation.
• In the model, four standards of proof are formulated as shown
on the next slide.
• It is assumed that there can be pro arguments as well as con
arguments with respect to a claim. It is also assumed that
arguments can be comparatively weighed so that one argument
is said to be stronger than another based on the evidence for
and against each of the arguments.
Carneades: Standards of Proof
• The scintilla of evidence standard is met iff there is one
argument supporting the claim.
• The preponderance of the evidence standard is met iff scintilla
of evidence standard is met and the weight of evidence for the
claim is greater than the weight against it.
• The clear and convincing evidence standard is met iff the
preponderance of the evidence standard is met and the weight
of the pro arguments exceeds that of the con arguments by
some specified threshold.
• The beyond reasonable doubt standard is met iff the clear and
convincing evidence standard is met and the weight of the con
arguments is below some specified threshold.
Carneades and Critical Questions
• Carneades has an argument mapping tool.
• Critical questions are modeled by Carneades as additional
premises corresponding to the critical questions of an
argumentation scheme.
• In the Carneades system, critical questions matching an
argument are reformulated as three types of premises called
ordinary premises, assumptions and exceptions (Gordon and
Walton, 2009).
• Assumptions are assumed to be acceptable unless called into
question. Exceptions are modeled as premises that are assumed
to be not acceptable, and can undercut an argument if found to
be acceptable.
How Carneades Models Critical
Questions for a Causal Argument
Premises of Argument from
Correlation to Cause (Carneades)
The Argumentation is Evaluated in
a Dialogue Using Burdens of Proof
• Evaluating argumentation in a case is a matter of adjusting
burdens of proof adjudicated at different stages of the dialogue.
• During the argumentation stage, as speech acts like arguments
are put forward, they need to be evaluated in light of how the
burden of proof shifts from one side to the other.
• For example if a claim is made, and the other party challenges
the claim, the first party has to support its claim with an
argument or else he has to retract the claim.
• There is also a global burden of proof set at the opening stage,
that determines how strong the argumentation on each side
needs to be in order to be successful in the dialogue.
Conclusions 1
• The argumentation in the pernicious anemia
case naturally breaks down into two dialogues.
• During the discovery dialogue, the feeding-ofliver treatment on human patients worked.
• Argument from correlation to cause was the
warrant for drawing an inference to a causal
hypothesis between these two sets of events.
Conclusions 2
• Later experiments, showed that a deficiency of
vitamin B12 was the cause.
• Only at this stage was an explanation given at an
adequate theoretical level to prove the
hypothesis about the cause of the disease and
answer all the critical questions.
• The investigation shifted to an inquiry dialogue
where enough evidence to prove that deficiency
of vitamin B12 was the cause.
Conclusions 3
• Traditional philosophy of science had drawn a
bright line between two stages, a discovery
stage and later proof or justification stage.
• The recent climate of opinion goes towards the
view that there is a continuous sequence of
argumentation from the one stage to the other.
• The conclusion of this paper seems to support
the latter view more strongly.
Some References
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Black, E. and A. Hunter, (2007). A Generative Inquiry Dialogue System, Sixth International Joint Conference on
Autonomous Agents and Multi-agent Systems, ed. M. Huhns and O. Shehory, 1010-1017.
Cooke, E. (2006). Peirce’s Pragmatic Theory of Inquiry: Fallibilism and Indeterminacy. London: Continuum.
Gordon, T. F. (2010). The Carneades Argumentation Support System, Dialectics, Dialogue and Argumentation,
ed. C. Reed and C. W. Tindale, London: College Publications.
Gordon, T. F., H. Prakken and D. Walton (2007). The Carneades Model of Argument and Burden of Proof,
Artificial Intelligence, 171, 875-896.
Gordon, T. F. and Walton, D. (2009). Proof Burdens and Standards, Argumentation and Artificial Intelligence,
ed. I. Rahwan and G. Simari, Berlin: Springer.
Jacovino, N. (2009). Red-Blooded Doctors Cure Anemia, The Harvard University Gazette, January 22, 1998.
Found Feb. 3, 2009 at: http://www.news.harvard.edu/gazette/1998/01.22/Red-BloodedDoct.html
Josephson, J. R. and Josephson, S. G. (1994). Abductive Inference: Computation, Philosophy, Technology. NY:
Cambridge University Press.
McBurney, P. and Parsons, S. (2001). Chance Discovery Using Dialectical Argumentation, New Frontiers in
Artificial Intelligence, ed. T. Terano et al. (Lecture Notes in Artificial Intelligence, vol. 2253). Berlin: Springer,
414-424.
Peirce, C. S. (1931), Collected Papers. Edited by C. Hartshorne and P. Weiss. Cambridge: Harvard University
Press.
Popper, K. (1962). Conjectures and Refutations: The Growth of Scientific Knowledge. Routledge: London.
Walton, D. Abductive Reasoning. Tuscaloosa: University of Alabama Press, 2004.