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

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 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 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 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 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 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 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 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 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 Cloud Chamber Credit:

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 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 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?