PY226: Philosophy of ScienceThe structure of scientific

revolutions

“The transfer of allegiance from paradigm to paradigm is a conversion experience”

Thomas Kuhn, The Structure of Scientific Revolutions

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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

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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

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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.

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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

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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

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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.

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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

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

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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

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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?

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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

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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

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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.

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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)

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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

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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

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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

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Cloud Chamber

Credit: www.scifair.org/projects/

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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

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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

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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?