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Science news “Becoming Human,” 3 part series by NOVA, began last Tuesday night and continues for 2 more weeks on Tuesdays. One hypothesis considered as an explanation of evolution of human mental capacities/brain size: climate change.

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science news
Science news

“Becoming Human,” 3 part series by NOVA, began last Tuesday night and continues for 2 more weeks on Tuesdays.

One hypothesis considered as an explanation of evolution of human mental capacities/brain size: climate change.

Earlier hypothesis emphasized bidpedalism, but that was before we found fossils of other hominids with relatively small brains.

Prediction? NY Times review: If we go through another period of increasingly hot and dry climate, our descendants might be much smarter … and have heads the size of basketballs 

science news2
Science news

Signs of early Homo sapiens in China?

Fossils over 100,000 years old found in southern China

Taken by Chinese scientists to challenge the hypothesis that the species originated in Africa and spread from there

Critics: Far too little evidence

A fragment of a lower jaw bone and some teeth

challenges to falsificationism
Challenges to Falsificationism

Complicating the logic of falsification

‘If H, then I’ is really ‘If [H & (A1… An)], then I’

More from Hempel:

‘I’ in ‘If H, then I’

is itself shorthand for ‘If C, then E’

where ‘C’ symbolizes some condition, and ‘E’ some event or phenomenon.

And ‘if C, then E’

is understood as “if some condition is brought about, then we will observe E .”

If this is correct, then the actual logic of falsification, on Hempel’s model, is

challenges to falsificationism4
Challenges to Falsificationism

If [H & (A1… & An)], then (if C then E)

Not E


Either not H & (A1… & An) or not C

On the left side, H may be incorrect – but it could be correct and one or more of the auxiliary assumptions is the problem (Brahe).

Or (as indicated by the right side), it may be that the conditions weren’t brought about (med students didn’t wash their hands...)

holism as yet another challenge to falsificationism
Holism as yet another challenge to Falsificationism

Duhem/Quine thesis: It is bodies of theory (or systems of theories), not individual hypotheses, that entail predictions.

If T (for some body of theory), then (if H, then I)

Not I


Not some one or more statements of Tor notH

Pierre Duhem: a bench physicist writing in the 1930s

W.V. Quine: philosopher of science writing from the mid twentieth century to its end


If T, then (if H, then I)

not I


Not some part of T or not H

Given what actually follows logically and empirically from ‘not I’, one needs to decide that ‘not H’ follows, rather than some part or whole of T; i.e., one has to choose to hold T firm and H infirm.

Are the choices arbitrary? Made on the basis of self-interest?

What are the consequences for objectivity?


Duhem’s examples (you do not need to memorize the details… just what he uses them to illustrate):

Neumann assumed a hypothesis that, if correct, was taken to predict that in an experiment involving a light beam reflected at a particular degree of angle, there ought to appear alternatively dark and light interference bands

Weiner, who challenged Neumann’s hypothesis, performed a test in which the predicted interference bands did not appear.

Had he, in fact, falsified, Neumann’s hypothesis?


Duhem’s examples:

No, according to Duhem, because Weiner had notonly used Neumann’s hypothesis to get the prediction and design the experiment: instead he brought and joined a lot of hypotheses to do both.

So what he actually demonstrated was that either Neumann’s hypothesis is incorrect, or one or more of the assumptions Weiner himself made, was/were incorrect.


In the case concerning whether light would travel faster in water than in air or vice versa as a test of Newton’s hypothesis that light consists of tiny projectiles vs. that light consists of waves moving through a medium:

It was the whole system Newton proposed that was under test, not the hypothesis that light is made up of projectiles

So, the moral is the same:

Nothing, logically or experimentally, stops us from accepting the hypothesis allegedly falsified and shifting the weight of the experimental contradiction to some other hypothesis or part of the larger theory that the experimenter assumes.

Both experiments Duhem cites had been taken as among the most decisive ones in optics; he is challenging this.


The model of Falsificationism as how scientists do or should reason, reflects “unfamiliarity with physics’ actual functioning”

Such people assume that “each one of the hypotheses employed in physics can be taken in isolation, checked by experiment, and then when many varied tests have established its validity, given a definitive place in the system of physics.”

“In reality, this is not the case. Physics is not a machine which lets itself be taken apart… physical science is a system that must be taken as a whole… If something goes wrong, if some discomfort is felt it, the physicist will have to ferret out … which “organ” needs to be remedied or modified without the possibility of isolating this organ and examining it apart.”


So-called crucial experiments:

Assume the logic of Reductio ad absurdum, an argument form that works in mathematics

But not, Duhem argues, in empirical science

Either P or Q 1. Either H1 or H2

Not P 2. Not H2

----------------- -------------------

Q H1

Recall Paley’s reasoning…


Reductio ad absurdum only works if one can list all the hypotheses that can account for some phenomena and then by experimental contradiction, eliminate all except one.

If you could do this, the resulting hypothesis would look like a certainty.

But you cannot. One can never be sure one has identified every possible hypothesis that might account for the phenomena.


An example: In the late 1980’s, researchers developed a drug predicted to be capable of thwarting the replication of the HIV virus implicated in AIDS.

H: “All things being equal … the drug will be effective”

In experiments, one group was given the drug and the other a placebo.

The initial trials (running over 2 years) confirmed the drug’s predicted success. But in the 3rd year, it stopped being effective.

Initial results (showing effectiveness) were taken to be mistaken

And the hypothesis was rejected by some


Then current theories suggested that it didn’t matter if the drug was stored and delivered in glass or plastic containers.

After the initial 2 year period, the drug was stored and delivered in plastic rather than glass containers.

Thus the conclusion that not H presumed the truth of this background knowledge – and it was wrong.

Storing the drug in plastic containers did affect it.


Critics of the Quine/Duhem (or Duhem/Quine) thesis argued that if correct, theories could never be refuted by evidence – but only by decisions made by scientists in the relevant field

This, they argued, leads to relativism and/or degrees of subjectivity that challenge scientific objectivity

Duhem and Quine: not so. It just means that science isn’t a machine.

Duhem: the physicist is more like a doctor making a diagnosis with available information, than a watchmaker who fixes a watch.


Later in the full chapter, Duhem argues that there are values (epistemic or cognitive) that guide the scientist’s choice

A list many cite includes:



Explanatory power

Empirical adequacy and/or success


part 2

Part 2

Introducing Kuhn

kuhn s the structure of scientific revolutions ssr
Kuhn’s The Structure of Scientific Revolutions (SSR)

First published in 1962, Kuhn’s SSR was named one of the 50th most important books of the 21st century by many lists (including The New York Times)

Kuhn: a bench physicist who became interested in the history of science (actual history) and argued that it did not match the reconstructions philosophers and historians of science, and scientists themselves, offered

While historians and philosophers of science (as well as scientists) emphasized revolutions in science as models of how science works, Kuhn emphasized what he called “Normal Science” – the kind of science most scientists engage in all of their lives that does not look what philosophers or historians of science, or even working scientists, hold up as “scientific method”

kuhn s ssr
Kuhn’s SSR

From “pre-science” to “normal science” to “crisis” to “revolution

Pre-science Lots of “schools” arguing over fundamentals

No agreement over what is the most important phenomena to be explained

No agreement on a basic theory or how the most basic phenomena are to be explained

The emergence of a “paradigm”

The beginning of a “normal science” (as opposed to a pre- science”) tradition

The emergence of a “paradigm” which

Solves a lot of puzzles (or promises to solve

puzzles) that need to be solved

Is open-ended enough to leave lots of work to do…

kuhn s ssr20
Kuhn’s SSR

Is like a “judicial decision” in that it invites further articulation

Brown v. Board of Education

“Separate but equal” is internally inconsistent

Originally about racially-segregated schools

But articulated to apply to other apparently “separate but equal” laws and practices



And other laws that cite “separate but equal” standards”

kuhn s ssr21
Kuhn’s SSR

Once a science community accepts a paradigm (Copernican astronomy, Newtonian physics, Darwinian natural selection, Relativity, Quantum physics…) the paradigm itself is unquestioned and work begins on

Puzzle solving: the paradigm indicates what problems are important (nature of the orbits of the planets, how natural selection works….) and this results in a

Puzzle-solving tradition

kuhn s ssr22
Kuhn’s SSR

Normal science (everyday, most of the time science) involves puzzle solving

Assume that any puzzle suggested by a paradigm is intrinsically important and

Has a solution that the paradigm, itself, supplies

Can be solved with sufficient ingenuity and/or creativity

Any failure to solve the puzzle is due to the researcher (her or his understanding of the puzzle, appropriate tests… but not the paradigm.

kuhn s ssr23
Kuhn’s SSR

Normal science (everyday, most of the time, science) is a closed-minded enterprise

Is not looking for anomalies

Seeks only confirming evidence of the Paradigm and any subsidiary hypotheses it suggests

Is an attempt to “fit nature into the boxes the Paradigm supplies”

Will only pay attention to anomalies (counter-examples) when

It is no longer reasonable to blame the individual researcher/test or

To wait for scientists of the next generation to find a solution or

there is a “competing paradigm”

kuhn s ssr24
Kuhn’s SSR

Kuhn’s “diagnosis” of how Popper “went wrong”

Not because (as Duhem article would suggest) that Popper didn’t know the history of science

But because he focused his attention on episodes of revolution

These, according to Kuhn, are rare and not “typical” of how science proceeds