Scientific Phylosophy - The Structure of Scientific Revolution

1. PY226: Philosophy of Science
The structure of scientific
revolutions
“The transfer of allegiance from paradigm to
paradigm is a conversion experience”
Thomas Kuhn, The Structure of Scientific Revolutions

2. 2
Kuhn’s Challenge: review
 The received view of science
 Science is cumulative
 Strict distinction between context of discovery
and context of justification
 Strict distinction between theoretical and
observational terms
 Science is objective: evaluation of observation is
value-free based on method

3. 3
Paradigms and ‘normal science’
 Kuhn’s analyses looked at the actual history
of science. Would Popper be interested in
history? Why not?
 Central concept for Kuhn: paradigm
 Paradigms involve two related ideas: (a)
disciplinary matrix and (b) exemplars

4. 4
Paradigms, disciplinary matrix and exemplars
 Scientists working in the same paradigm share
background beliefs, assumptions and values.
 They agree on what areas are worthwhile
investigating, what methods to use, what
counts as evidence, and so on.
 ‘Exemplars’ are used to train scientists; they
are the textbook cases in which particular
theories are worked out or particular laboratory
techniques are used.

5. 5
Paradigms and Normal science
 What happens in a paradigm?
 Puzzle solving: All paradigms have cases that
cannot be easily accommodated—the orbit of
Uranus before the 1850s in Newtonian
mechanics for example
 Scientists strive to solve those puzzles as
well as to extend the paradigm as far as
possible to other domains

6. 6
Normal Science vs. Falsification
 Normal science is
‘conservative’
because the idea is
NOT to test the
paradigm. The
paradigm is not
(usually) up for
grabs.
 On Popper’s view,
scientists should
work to reject
theories

7. 7
Normal science and crisis
 In ‘normal science’, anomalies—phenomena
that the theory cannot accommodate—are
typically ignored while scientists go about
fine-tuning the paradigm.
 In time, however, they accumulate.
 A ‘crisis’ ensues in which confidence in the
old paradigm is shaken. Some scientists start
to look for alternatives.

8. 8
Crisis and revolution
 In proposing alternatives, the shared
assumptions and beliefs may be given up
 Kuhn calls this period ‘revolutionary science’
 Eventually, a successor paradigm emerges

9. 9
A pictorial schema of Kuhn’s idea of paradigm shift
from psychlops.psy.uconn.edu/eric/291/291_philosci..

10. 10
Examples of paradigm change
 Kuhn calls changes in paradigms ‘paradigm
shifts.’
 From Ptolemaic to Heliocentric astronomy:
the problem of ‘epicycles’ to explain
retrograde motion of planets
 Possible example: pre-Keynesian economics
and Keynesian economics

11. 11
Are paradigm shifts ‘rational’?
 Kuhn allows that there may well be good
reasons to change paradigms but they alone do
not cause the change.
 Other factors that may play a role: peer
pressure, pressure to get funding, etc.
 “The transfer of allegiance from paradigm to
paradigm is a conversion experience which
cannot be forced.”
 What does ‘conversion experience’ suggest?

12. 12
Living in different paradigms
 Since fundamental beliefs and assumptions
are up for grabs in articulating a new
paradigm, successive paradigms, for Kuhn,
are incommensurable. (Incommensurable:
meaning no common measure.)
 One example: ‘planet’ in Ptolemaic and
Copernican astronomy

13. 13
Consequences of Kuhn’s account
 Consequences of Kuhn’s view are:
a) Science does not proceed in a linear way
b) Science is not cumulative
c) Science need not be rational

14. 14
Observation and Theory distinction
 Pre-Kuhn view of observation: neutral (in order
that they can play the role of either refutation or
corroboration)
 Kuhn argues that observation data are informed
by theoretical assumptions. What scientists ‘see’
is influenced by their beliefs.
 This is called theory-ladenness of observations.

15. 15
Theory-ladenness of observation
 Kuhn is following the ideas of N.R. Hanson.
 Hanson: “Seeing is not only the having of a visual
experience; it is also the way in which the visual
experience is had … observation of X is shaped
by our prior knowledge of X” (Hanson cited in
p.111)

16. 16
Theory-ladenness of observation
 ‘Theory-ladenness’ can be interpreted as
follows:
 1. the language we use to describe our
observations are theory-laden.
 2. the concepts we hold (theories we accept)
inform the content of our observations

17. 17
Theory-ladenness of observation
 An example of the first interpretation is the
sentence “an electronic current is flowing
through the parallel circuit”
 This observational sentence is based on
inferences using standard beliefs about
electronic currents and would not be made by
individuals who do not have those concepts

18. 18
Theory-ladenness of observation
 The second interpretation suggests that
perception is ‘plastic’ and is a more radical
interpretation
 If true, it would suggest that two individuals
with different beliefs will not be seeing the
same thing
 Example: tracks in cloud chamber as
evidence for positrons not cited before the
theoretical postulation in 1928

19. 19
Cloud Chamber
 Credit: www.scifair.org/projects/

20. 20
Theory-ladenness of observation
 Counter-argument to the second interpretation
 The ‘seeing’ and ‘seeing as’ distinction
 Some one without the relevant concepts of ‘cloud
chamber’ and ‘positron’ will not see the tracks as
trails left a positron. Nonetheless, they still see
the marks left on the photograph
 The counter-argument is basically an argument
for the first interpretation

21. 21
Theory-ladenness of observation
 There are examples which suggests that what
we see is immune from our beliefs. Consider: the
Müller-Lyer illusion below
 The radical claim that perception is plastic
cannot be easily held

22. 22
Theory-Ladenness of observation
 Question to think about: Even if observations
are not totally free of theory, would that be
enough to show that observations cannot be
used as ‘objective’ evidence to decide
between theories?