novel prediction and the underdetermination of scientific theory

Richard Dawid
Univ. of Vienna
A General Strategy
• To the Bayesian, confirmation is an increase of the probability
of a theory’s truth due to empirical data.
P(T |E)/P(T)= P(E|T)/P(E)
• Per se, it does not matter whether the data has influenced
theory construction or not.
 Novel confirmation does not directly raise confirmation value.
• However, the observation that novel confirmation took place
can itself constitute data which confirms a statement that in
turn raises the probability of T.
Some suggested ideas
• A number of authors have used that strategy and proposed
various qualities which are to be assessed by observing novel
• Patrick Maher: novel confirmation confirms that the method
of theory construction (rather than the theory itself) is good.
• Hitchcock & Sober: n.c. indicates that there is no overfitting.
• Kahn,Landsberg,Stockman: n.c confirms that the scientist who
constructed the theory before confirmation is competent.
• Eric Barnes: n. c. confirms that the scientist who endorsed the
theory before confirmation is capable.
The same principle, a different suggestion
• Claim: Looking for novel confirmation can lead to an
assessment of a crucial characteristic of the scientific context:
the underdetermination of scientific theory building by the
available data.
• In a number of scientific contexts, in particular in modern
physics, this assessment constitutes the most important extravalue of novel confirmation over accommodation.
• This does not imply that other construals of an extra-value of
n. c. are false. N.c. may well work at various levels.
However, we suggest that underdetermination plays a pivotal
role in the case of physics.
Underdetermination of Scientific Theory Building
all possible evidence
available evidence
Quine [‚reasons for Sklar, Stanford
indet. of transl.‘]
(transient underdet.)
van Fraassen
Scientific Underdet.
The Framework
• Assumption: a priori, scientists can’t be expected to construct
the theory that will be empirically successful in the future.
 If many scientific theories are possible which
 fit the available data
 satisfy “scientificality conditions” C
 give different predictions regarding upcoming experiments
then chances are high that scientists find the wrong theory.
(In the simplest model, if there are i such theories, chances
are 1/i.)
Alluding to additional criteria like simplicity, beauty, etc. adds
to the conditions C but does not change the argument.
The Argument
• Inversely, if novel predictive success occurs, that indicates
limitations to scientific underdetermination.
• Meta-inductive reasoning then leads to the inference that, if
limitations to scientific underdetermination frequently occur
at some level at one stage, they are likely to occur at following
stages as well.
=> therefore, the observation of novel confirmation raises the
probability for the theory’s truth.
 To the contrary, accommodation does not tell anything about
scientific underdetermination.
o In the extreme case where no limitations are assumed, P(T)=0 and no
confirmation occurs.
o If one assumes some limitations a priori, there is some confirmation
but it is weaker than in the case of novel confirmation.
Comparison with other Approaches (1)
Example: The standard model of particle physics (SM)
The Higgs is the last of many SM predictions. All others were
successful. SM is strongly believed in due to its n.c. successes.
 SM was developed in the early 60s, got first n.c. in the mid 70s and
since then is believed in by most physicists.
 Situation today quite different than back then. Lots of new
 Developers and early endorsers back then are not the leading
experts today.
o relating an evaluation of developers/ endorsers to theory
assessment seems problematic.
– People don’t t believe in the SM today because n.c. has shown Weinberg’s
competence in the 1960s.
– Whether or not there were early endorsers does not matter either.
=> It seems far more plausible that n.c. evaluates the scientific context
rather than scientific agents.
Comparison with other Approaches (2)
• Hitchcock and Sober do not work in the SM case either.
– Developing the SM is a matter of finding a general scheme
that solves general consistency problems. Overfitting plays no role.
• Assessment of scientific underdetermination adresses
precisely the context of finding consistent solution and asking
how many alternative solutions exist.
• The SM shows these points with particular clarity
– Due to the strong theoretical constraints, it highlights the importance
of consistency.
– Due to the long time periods, the problems of Kahn et al and Barnes
become more conspicuous.
However, the use of n.c. seems characteristic of fundamental
Distinction between AoU and other Ideas
 Scenario:
– First one theory A is developed and endorsed.
– Then A gets empirically confirmed by data D.
– Then someone else discovers that theory B also reproduces data D.
? Question: does novel confirmation favour A over B?
• Many approaches (Kahn et al., Hitchcock&Sober) would say
• AoU says no: underdetermination is the same for A and B.
Reduction of P(T) due to new known alternative at the same
level as comparison between A and B.
o When consistency is a dominating factor, AoU looks good.
o When not, other approaches fare better.
! However: predictive power seems strongest when consistency
is an issue.
• Assessment of scientific underdetermination
constitutes a crucial reason for the higher
confirmation value of novel confirmation.
• It applies in contexts where questions of consistency
are important in theory building.
• Arguably, those are the contexts where novel
confirmation occurs most frequently.

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