Kuhn on Revolutionary Science

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

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.

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.”

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.

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.

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. …”

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.

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

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.

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.

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.

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”?

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.

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.

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?

“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.

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.

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.

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.

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’.

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).

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.
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).

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 stainsàcancer).

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.

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.

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.

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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