KUHN ON REVOLUTIONARY SCIENCE
At any given time during normal science,
there are outstanding problems.
 Kuhn calls these “anomalies”.
 They are predictions that the paradigm
gets wrong, events it can’t explain, etc.
Most of the time, scientists note these
problems but keep working.
 This is because the paradigm overall is
so successful—anomalies will be
solved, scientists hope, in the future.
Note how this contradicts Positivism/Popper
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Crisis & revolution
Eventually, however, anomalies may build
up to the point where they are no longer
seen as unsolved puzzles: the paradigm
itself is questioned.
 At this point, science enters a crisis
phase: standard assumptions are no
longer trusted.
What happens?
 The paradigm “blurs” and “loosens” as
scientists attempt to find new categories
and laws that will handle the anomalies.
Three possibilities:
1. The old paradigm is rescued (after
modification).
2. The problem is too big: ignored.
3. A new paradigm arises—able to solve
the problems.
Option #3 is a scientific revolution. This is
how science moves forward.
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Progress?
“Does science progress?” = “Are new
paradigms better than old ones?” Do new
paradigms get closer to the truth or are they
just a new way of doing things?
“Like the choice between competing political
institutions, that between competing paradigms
proves to be a choice between incompatible modes of
community life. Because it has that character, the
choice is not and cannot be determined merely by the
evaluative procedures characteristic of normal
science, for these depend in part upon a particular
paradigm, and that paradigm is at issue. When
paradigms enter, as they must, into a debate about
paradigm choice, their role is necessarily circular.
Each group uses its own paradigm to argue in the
paradigm’s defense …
The man who premises a paradigm when arguing in
its defense can … provide a clear exhibit of what
scientific practice will be like for those who adopt [the
paradigm] … whatever its force, the status of the
circular argument is only that of persuasion. It cannot
be made logically or even probabilistically compelling
for those who refuse to step into the circle.”
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In other words:
Scientific reasoning exists within a
paradigm.
Hence, we cannot use scientific arguments
to justify the claim that a new paradigm is
superior because:
Such arguments only get their force within
a paradigm.
What does this tell us?
 Scientific progress is not cumulative: the
switch from one paradigm to another is
not a smooth process of addition but
one of replacement.
 The usual scientific methods of settling
disputes cannot help when deciding
between paradigms. It is not a simple
matter of experiment and observation to
see which is right.
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Not cumulative
Different paradigms can’t live together
because one a new one only arises when
an old one is seen to get things wrong.
The new one is accepted because it
explains what the old one was unable to.
Hence, the two must be in conflict at some
level.
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Rationality?
Does that mean that the switch from one
paradigm to another is not a matter of
rational persuasion? If not, then what?
“[E]ach paradigm will be shown to satisfy
more or less the criteria that it dictates for
itself and to fall short of a few of those
dictated by its opponent. … Like the issue of
competing standards, that question of
values can be answered only in terms of
criteria that lie outside of normal science
altogether, and it is that recourse to external
criteria that most obviously makes paradigm
debates revolutionary. …”
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Incommensurability
“No common measure”
 The categories and concepts of a new
paradigm may be so different from those
of an older paradigm that there is no
way to compare them.
For example, Einstein’s theory not only has
different equations from Newton’s, but is
also such that the meanings of the terms
“mass”, “space” and “time” are different.
 There is third standard, no “neutral”
perspective that allows us to step
outside each theory and compare them.
 The best we can say is that one
paradigm solves problems in a way that
attracts scientists from the old paradigm.
Also, there may be no terms in one
paradigm to refer to items mentioned in
another. E.g.: no term for ‘phlogiston’ in
current chemical theory.
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Some thoughts on Kuhn’s views
Does the very idea of incommensurable
paradigms threaten the notion that science
is a rational activity?
Not obviously:
 Perhaps the new paradigm explains
everything the old one does plus more.
 E.g. Lakatos’ picture
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Two sense of ‘paradigm’
Notice that there are two ways in which we
can understand a paradigm:
1. As an impressive achievement: a
successful technique, theory or
method that wins followers.
Or
2. As a set of shared values: standards,
assumptions, priorities, textbooks,
journals, etc., which define “scientific”.
Sense #1 is no threat to science as a
rational process:
 The impressive achievement may, after
all, be better and hence a more rational
choice.
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Shared values
Consider the second sense of paradigm:
 To succeed in science you must
impress the right people, write winning
grant proposals, etc.
 To even be considered a scientist you
must demonstrate shared values.
Does this mean science proceeds in an
irrational manner? Perhaps not:
 Science is a human activity and subject
to human failings.
 However, its methods might still “filter
out” these lapses and, over time, favour
the most rational.
So why was Kuhn thought to be a threat to
rationality?
The answer lies in his notion of paradigm
change and incommensurability.
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Internal vs. external questions
Within a paradigm, Kuhn believes science
can and should exhibit intellectual virtues:





Accuracy (fit data, predictions)
Consistency (internally & with others)
Broad scope
Simplicity
Fruitfulness: novel predictions/ideas
However:
 These virtues can’t decide between
paradigms: they each get a hold only
within a paradigm.
Differences between paradigms make a
point-by-point comparison impossible:
 You just have to “learn the new
language” and adopt the new
techniques/beliefs.
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Conversion and “Gestalt switch”
Adopting a new paradigm is learning to see
the world in a new way.
It is a conversion: you see the strengths
after you convert, not before.
 You can’t reason from one viewpoint to
another.
 There is only one image (fact) but two
ways to see it:
Can we compare them to see which one is
“right”?
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Non-rationalism
Some have thought that Kuhn’s ideas
render scientific progress a matter of
conversion not rational persuasion.
It is not that scientific progress is irrational:
 It doesn’t involve ignoring compelling
evidence or accepting contradictions.
It is just that change from one paradigm to
another is not a matter of following timeless
principles or unchanging rules.
Faced with a crisis, one must make a
decision under uncertainty.
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Risky decisions
Suppose one is faced with two paradigms,
P1 and P2, both of which attempt to explain
the physical world.
 P1 does a good job with some of the
data but not others; vice versa with P2
 There is no set of principles to decide
which is better from the “outside”
So, the choice is underdetermined by the
evidence. What is one to do?
 One must take a risk: get with the new
program or place your confidence in the
old one.
 This is risky but one must do it.
It is similar to trusting your ‘gut feeling’ when
the evidence doesn’t favour one side over
the other.
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Rationality and Paradigms
While accepting a paradigm is, according to
Kuhn, a kind of conversion experience he
later came to insist that one can have better
(or worse) reasons for undertaking a
conversion.
 The point seems to be that no such
reasons can force or guarantee a
conversion.
Kuhn does claim that shared criteria can
guide the scientific process between
paradigms.
 But what are we to make of these
shared criteria between paradigms?
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“Depth” of revolutions
McMullan points out that Kuhn’s examples
of scientific revolutions are not equally
disruptive.
Some are quite shallow, such as the
discovery of x-rays—this did change the
way scientists proceeded, but it didn’t shake
the foundations.
Others are moderately deep: they involve
new, more comprehensive theories but
don’t overthrow the basic epistemological
principles of the debate:
 E.g.: phlogiston theory of combustion
replaced by oxygen theory.
 Both sides would agree on what counts
as evidence or what should be tested.
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Deep revolutions
Other revolutions really do change what
counts as a good theory or genuine
evidence:
 Aristotelian to Galilean physics
 Ptolemaic to Copernican Astronomy
So not all revolutions are threats to shared
epistemic standards of evaluation.
Even so, Kuhn came to defend the idea that
the five theoretical virtues do function as
relatively permanent criteria for the
evaluation of theories.
 What changes is the weight assigned to
any one of them and how they are
interpreted.
 But there is relative stability here (p.
115).
If not, there really would be no rationality
involved in paradigm change.
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Stability and deep revolutions
It seems, then, that truly deep revolutions
don’t in fact occur—there is always some
level of shared epistemic value.
That is, even though, say, Aristotelians and
Galileans disagree deeply about what
particular observations count as evidence:
 They both agree that a good theory
needs to be accurate, simple, fruitful etc.
These are ‘meta-values’ that remain
constant.
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McMullan’s challenge
A key point, however, is that these values
themselves are simply the ones we find
useful.
 There is no sense in which they are
objective guides to the truth or the deep
structure of reality.
McMullan asks: How can Kuhn explain the
stability of these values?
 Why don’t they change?
Kuhn has no clear answer to this, which
suggests his views on the meta-values need
further development.
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Justifying the values
McMullan argues that not all of Kuhn’s
meta-values are on equal footing.
Predictive accuracy and explanation
appear to be the goals of science.
 The other virtues are valued as means
to these ends.
The two goals are definitive of science:
 So, they have/require no justification—to
reject them is to step outside the
scientific enterprise.
 The rest are justified in terms of the
ends.
This is a story that Kuhn ought to tell,
argues McMullan. It also conflicts with
Kuhn’s idea of science as a ‘cluster
concept’.
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No truth (yet)
McMullan admits that this is no proof that
accuracy and explanation are indications
that a theory is true.
The upshot is just that:
 Historically, properties of theories such
as simplicity have been valued because
they seem to serve accuracy and
prediction
 Epistemologically we can expect, e.g.,
simple theories to be more accurate and
explanatory (but this requires
argument).
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Rationality and verisimilitude
So, it seems (and McMullan argues) that
Kuhn weakened his stance and came to
allow for inter-paradigmatic rationality.
 Science can progress from one
paradigm to another according to
external standards of evaluation.
But he denies that science progresses by
better approximating the truth.
 Success in puzzle-solving gives us no
reason to think that we have a more true
theory than before.
 The ontologies of competing paradigms
are discontinuous so later ones are not
improvements on earlier ones.
McMullan sees a tension between these
components of Kuhn’s later stance.
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Copernicus and Ptolemy
Consider the move from Ptolemaic to
Copernican astronomy:
 At first, each had equal predictive
accuracy (more or less).
 But, what moved astronomers was an
aesthetic appreciation of Copernicus’s
theory, argues Kuhn.
But McMullan disagrees:
 Copernicus’s theory was accepted
because it could explain phenomena
that Ptolemy couldn’t.
 It provided the cause (heliocentric
motion) of what was observed (shades
of Salmon here).
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Explanation and causes
Kuhn suggests that Ptolemy could explain
all the observed phenomena.
McMullan counters:
 He could attribute no causes to what
was observed.
 He could construct principles that
allowed him to predict phenomena, but
they became quite ad hoc.
 A principle that allows for successful
prediction is not necessarily an
explanation (e.g. yellow stainscancer).
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Explanation and realism
So, McMullan concludes that:
Copernicus’s theory was better able to
explain because it made causal sense of
observations, and such sense gives one
reason to believe a theory is true.
 I.e. it gives us reason to believe the
earth really does revolve around the
sun.
It is not, as Kuhn suggests, merely aesthetic
features such as simplicity or elegance that
turned people in favour of Copernicus.
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Rationality and realism
So, puzzle solving (including predicting
accurately) is not the only marker of a
successful theory/paradigm.
 If that were the case, then the move
from Ptolemy to Copernicus could only
be aesthetic, not rational.
But the move was rational because there
was reason to think the latter was true—it
had found the real causes of what we
observe.
 If not, it would be a miracle that
predictions based on that explanation
turned out to be accurate.
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Explanation and prediction
What this shows, argues McMullan, is that
explanation and prediction are
epistemologically valued because they are
seen as indicators of truth.
Also, explanatory power is more important
than simple predictive accuracy:
 Between two equally predictive theories
we rightly choose the more explanatorily
powerful.
 We will choose a more explanatorily
powerful one that has less predictive
accuracy.
Why? Because causal explanation gives us
reason to believe a theory is true.
 Otherwise, successful prediction on its
basis is a miracle.
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Summary
In sum, McMullan argues that Kuhn’s
position has two major problems:
First, it can’t explain why we have relatively
stable epistemic values.
Secondly, it tells us that even rational
moves give us no reason to believe a new
theory is likely to be true or truer than the
old theory.
 But it is impossible to defend the idea of
rationality (adhering to stable values)
while simultaneously denying realism,
as the Copernican case shows.
We could sum up McMullan’s view this way:
epistemic virtues are valued because they
are seen to lead to truth.
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