P160 Duhem and Quine

PHIL 160PHIL 160PHIL 160PHIL 160


Underdetermination of theory by data




Holism in testing


Holism in testing



Holism in testing

Meaning holism


Holism in testing

Meaning holism

THEORYTHEORY

• What kind of stuff is in the world

• What kind of stuff is in the world• How that stuff behaves• How that stuff behaves



INDUCTIVE LOGICINDUCTIVE LOGIC

Narrow Inductivist Picture of Science:Narrow Inductivist Picture of Science:

Collect data from

experience

Collect data from

experience

Derive generalizatio

ns

Derive generalizatio

ns


Form hypothesesForm hypotheses

Hempel’s Picture of Science:Hempel’s Picture of Science:

1. Find test implications.2. Set up test conditions.3. See what happens.

1. Find test implications.2. Set up test conditions.3. See what happens.

Test hypothesesTest hypotheses

(data + imagination)(data + imagination)


1. If H is true, will observe I under test conditions.

2. Set up test conditions.3. Observe not-I.

H is falseH is false




Test hypotheses - negative testTest hypotheses - negative test


Problem of induction

Problem of induction







Test hypotheses - negative testTest hypotheses - negative test

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1. If H1 and H2 and H3 and H4 and … are true, will observe I under test conditions.


H1 or H2 or H3 or H4 or … is false

1. If H1 and H2 and H3 and H4 and … are true, will observe I under test conditions.


H1 or H2 or H3 or H4 or … is false

Test group of hypotheses



Individual hypotheses don’t always generate testable predictions.

H1: “Cadaveric matter causes childbed fever.”


Need auxiliary hypotheses to generate testable predictions:

H1: Cadaveric matter causes childbed fever.H2: Cadaveric matter is transferred from cadavers to patients via hands, instruments.H3: Washing hands, instruments in chlorinated lime will remove or destroy cadaveric matter.


Negative test - Negative test -




Negative test - there is a problemSOMEWHERE in thegroup of hypotheses





Some individual hypotheses are testable:

H: Mars has a triangular orbit.


1st law of motion: If there is no force acting on a body, the momentum of that body will remain constant.

1st law of motion: If there is no force acting on a body, the momentum of that body will remain constant.

Newton’s group of hypotheses



2nd law of motion: If there is a force acting on a body, that body will accelerate by an amount directly proportional to the strength of the force and inversely proportional to its mass.

2nd law of motion: If there is a force acting on a body, that body will accelerate by an amount directly proportional to the strength of the force and inversely proportional to its mass.




3rd law of motion: If one body exerts a force on a second body, then the second body exerts a force on the first body that is equal in strength and opposite in direction.

3rd law of motion: If one body exerts a force on a second body, then the second body exerts a force on the first body that is equal in strength and opposite in direction.




Law of universal gravitation: Any two bodies exert attractive forces on each other where the forces are in the direction of the line connecting the bodies and are proportional to the product of their masses divided by the square of the distance between them.

Law of universal gravitation: Any two bodies exert attractive forces on each other where the forces are in the direction of the line connecting the bodies and are proportional to the product of their masses divided by the square of the distance between them.




3 laws of motion + law of universal

gravitation


gravitation

No testable predictions!No testable predictions!





gravitation+ auxiliary hypotheses

about masses, positions of planets and sun




Predictions of planets’ orbits

Predictions of planets’ orbits




But where?

But where?






Bad prediction of Uranus’s orbit



















Missing a planet?

Missing a planet?




Astronomers changed auxiliary hypothesisabout how many planets, left Newton’s laws & UG unchanged.This fixed bad prediction of Uranus orbit.

New planet (Neptune) observed by telescope.








Bad prediction of Mercury’s orbit





First attempt: stick another planet in

(“Vulcan”) betweenMercury and Sun.




No repeatable observations of this new planet.








(Possible aux. hypothesis:(Possible aux. hypothesis:the new planet is the new planet is

invisible!)invisible!)


(Possible aux. hypothesis:(Possible aux. hypothesis:the new planet is the new planet is

invisible!)invisible!)














Bad theory?

Bad theory?




Duhem says scientists must

rely on “good sense”

Duhem says scientists must

rely on “good sense”

No set rule for how to fix group of hypotheses that makes a bad prediction.

No set rule for how to fix group of hypotheses that makes a bad prediction.


Holism in testing important in observations made with scientificinstruments.

Group includes hypotheses about themeasuring device.


Theory predicts: room temp chickenis a good host for salmonella.

Test prediction with microscope.


In the group of hypotheses:

Theory about salmonella growth.Theory of the microscope.

Bad prediction could mean a problemwith either theory (or both)


Quine: Hypotheses are tested in groupsand the group includes all humanknowledge claims (including meaningsof terms).

“Meaning holism”

Can’t test hypotheses in isolation, andchanges in one hypothesis can prompt changes throughout whole logical structureof the theory.


What does this have to do with the Twin Earth thought experiment?


Is the stuff from Twin Earth water?

Devise observations that could helpyou distinguish water from not-water.



For every test, performs identically to water.Thus, reasonable to conclude (1600)it is water.



New test: elemental analysisWater from Earth: H2OStuff from Twin Earth: XYZ

But is Twin Earth stuff water?


Is the stuff from Twin Earth water?Because of meaning holism, this depends on the choices you makein evaluating the group of hypotheses.

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1. Water is the stuff found in rivers, lakes, streams, and aqueducts that humans drink, cook with, bathe in, swim in, etc.

1. Water is the stuff found in rivers, lakes, streams, and aqueducts that humans drink, cook with, bathe in, swim in, etc.

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2. Water displays certain regular behaviors (boiling under certain specified conditions, freezing under certain specified conditions, dissolving particular amounts of certain substances, etc.).

2. Water displays certain regular behaviors (boiling under certain specified conditions, freezing under certain specified conditions, dissolving particular amounts of certain substances, etc.).

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3. Although water from the ocean, water from a stream, water from a well, rainwater, etc., may differ in their impurities (salt, mud, etc.), they all count as water; that is, the substance containing these different impurities is the same.

3. Although water from the ocean, water from a stream, water from a well, rainwater, etc., may differ in their impurities (salt, mud, etc.), they all count as water; that is, the substance containing these different impurities is the same.

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4. Water’s behavior is a result of what it is made of.

4. Water’s behavior is a result of what it is made of.

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5. If two samples display different microstructure (e.g., different elemental composition), they must be samples of different substances.

5. If two samples display different microstructure (e.g., different elemental composition), they must be samples of different substances.

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6. Substances with different microstructures will display different macroscopic behavior.

6. Substances with different microstructures will display different macroscopic behavior.


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Group of hypothese

s

Group of hypothese

s


2 1

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Drop theseDrop these

21

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4Group of hypothese

s

Group of hypothese

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Add “Water is H2O”

Add “Water is H2O”

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2

Drop theseDrop these

Group of hypothese

s

Group of hypothese

s

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Courtesy of the Frances Loeb Library, Graduate School of Design, Harvard

University


University



University


University


“Any statement can be held to be true come what may, if we make drastic enough adjustments elsewhere in the system.”

“Any statement can be held to be true come what may, if we make drastic enough adjustments elsewhere in the system.”

P160 Duhem and Quine

Education

Transcript of P160 Duhem and Quine