The trajectory of reasoning so far about scientific method/reasoning…

Note: this now includes parts 1 and 2 of lecture (Duhem and Kuhn). If you accessed an earlier version, use this one for tomorrow’s lecture.

The trajectory of reasoning so far about scientific method/reasoning…

Hume’s problem of induction and his conclusions…The rejection of the idea that there is a “logic” to

discovery (and the acceptance of the idea that how hypotheses come about isn’t important)

Emphasis on the logic of justification (testing)Hempel: Sophisticated (or “wider”) inductivismand responses to the limits of inductive reasoningPopper: avoid induction altogether; focus on the logic of falsification…

Challenges to Falsificationism

Complicating the logic of falsificationHempel: Some predicted outcome, I, is not entailed by an individual hypothesis, H, in isolation; it is entailed by H and one or more auxiliary assumptions (A1 … An).And ‘I’ is itself shorthand for “If conditions C are brought about, then an event E will occur.”

So, the actual logic of falsification is

Challenges to Falsificationism If H & (A1… & An), then (if C then E)Not E----------------------------------------------Either not H & (A1… & An) or not COn 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...)

Or it could be that one of the assumptions of the “if/then” sort is itself wrong

And then there’s the history of science

Problems facing the Copernican hypothesis, yet it is accepted.

Problems facing Darwin’s hypothesis of natural selection, yet it is accepted.

Cases of “planetary misbehavior” that result in the discovery of new planets, not rejection of Newtonian theory.

Did scientists demonstrate a lack of objectivity in these cases… or is Popper’s model of scientific practice incorrect?

HolismHolism: Popper is incorrectDuhem/Quine thesis: It is bodies of theory (or

systems of theories or of hypotheses), NOT individual hypotheses, that entail predictions.

If T then (if H, then I)Not I---------------------------------------------

So, not some one or more statements of T or not H

Pierre Duhem: a bench physicist writing in the 1930s

W.V. Quine: philosopher of science writing in the 1960s.

Holism If T, then (if H, then I) not I ------------------------------ Not some part of T or not H

Given what actually follows logically from not I: To decide that ‘not H’ follows, rather than some part or whole of

T, is to choose to hold T firm and H infirm. Neither logic nor the experimental results dictates that H

is the problem, or dictates which (some or all of T or H) to hold and which to reject.

Holism Duhem’s examples (you do not need to memorize the

details… just his points):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?No, because Weiner had not only 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.

Holism Duhem’s examples (you do not need to memorize the

details… just his points): In each case he considers (the other 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), 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 that the experimenter assumes.

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

Holism The logic of falsification, and 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 [its functioning] 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.”

Holism So-called crucial tests: Assume the logic of reductio ad absurdum, an argument

form that works in mathematics but not in empirical science:Either H1 or H2 If H1, then INot I----------H2

Holism First problem: I does not follow from H1 alone If not I occurs, it

does not pinpoint that H1. As importantly, 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.

So, suppose, as in many such “crucial tests,” you are comparing 2 hypotheses and show that one is falsified by experiment.

Does that make the other certain? Not in science! One can never be sure one has identified every possible

hypothesis that might account for the phenomena (as we saw with Paley!)

Holism An example of Holism: 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 untrustworthy

So not H

Holism So not H Then current knowledge indicated 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.

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 The Structure of Scientific Revolutions (SSR)

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

Lots of “schools” arguing over fundamentalsNo agreement over what is the most important phenomena to be

explainedNo 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” whichSolves 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 The Structure of Scientific Revolutions (SSR)

Is like a “judicial decision” in that it invites further articulation Brown v. Board of Education

“Separate but equal” is internally inconsistentOriginally about racially-segregated schoolsBut articulated to apply to other apparently “separate

but equal” laws, theoriesGenderSexualityAnd other laws that cite “separate but equal”

standards”

Kuhn’s The Structure of Scientific Revolutions (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 The Structure of Scientific Revolutions (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, suppliesCan be solved with sufficient ingenuity and/or

creativtyAny 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 The Structure of Scientific Revolutions (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 orTo wait for scientists of the next generation to find a solution or

there is a “competing paradigm”