Lecture Eight Scientific Explanation

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Lecture Eight Scientific Explanation

• Dr Emma Tobin
• Philosophy
• Bristol

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• Is explanation subjective or objective?
• How do we know when we have found the best
  explanation?
• Is scientific explanation linked to truth?
• Do some kinds of explanation reduce to other
  kinds of explanation?

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Epistemology Metaphysics

• An account of scientific explanation could
  justify our claim to scientific knowledge allow
  strict demarcation. (Epistemology)
• The relationship between explanation causation
  could influence our metaphysical commitments
  about the real structure of the world.
  (Metaphysics)

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What and Why Questions ?

• What are the properties of Gold?
• What is the primary cause of lung cancer?
• What is a peppered moth?
• What is the structure of the heart?

• Why does Gold expand when heated?
• Why do smokers die younger?
• Why are moths pepper coloured?
• Why does the heart beat?

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Answering What questions - Descriptions

• Q What are the properties of Gold ?
• A Gold is yellow, malleable, ductile metal. It
  is a good conductor of heat and electricity and
  has atomic number 79.
• Q What is the primary cause of lung cancer?
• A Smoking.
• Q What is a peppered moth?
• A The peppered moth (Biston betularia) is a
  temperate species of night-flying moth.
• Q What is the structure of the heart?
• A The heart is a pear shaped, muscular organ in
  vertebrates, which pumps blood through the blood
  vessels by repeated, rhythmic contractions.

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Answering Why Questions - Explanations

• 1) Nomological Explanation (Laws)
• Q Why does Gold expand when heated?
• A All metals expand when heated (Law) Gold
  is a metal.
• 2) Causal Explanation
• Q Why do smokers die younger?
• A Smoking causes cancer.
• 3) Evolutionary Explanation
• Q Why are moths pepper-coloured?
• A Pepper-coloured moths had a selective
  advantage over white-coloured
• moths in the industrial revolution.
• 4) Teleological Explanation
• Q Why does the heart beat?
• A The Function of the heartbeat is to circulate
  blood.

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• (1) Is there a single form of explanation that is
  characteristic of all these varieties of
  explanation.
• (2) What is the logical form of scientific
  explanation?

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• To explain the phenomena in the world of our
  experience, to answer the question why?, rather
  than only the question what, is one of the
  foremost objectives of all rational inquiry and
  especially, scientific research in its various
  branches strives to go beyond a mere description
  of its subject matter by providing an explanation
  of the phenomena it investigates.
• Hempel Oppenheim (1948) Philosophy of Science
  (Course Booklet)

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Nomological Explanation The Covering Law Model
(Hempel)

• To explain an event is to subsume it under a law
  of nature.
• All scientific explanations have the structure of
  an argument (i.e. a set of premises followed by a
  conclusion.)
• The premises tell us why the conclusion is true.
• The premises will include at least one general
  law of nature.

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Deductive Nomological (D-N) Inductive
Statistical (I-S)

• D-N
• L1 L2 L3 Laws
• C1 C2 C3 Initial conditions
  (Explanans)
• F1 Fact- to- be- explained
  (Explanandum)

• I-S
• P1 P2 P3 Probabilistic Laws
• C1 C2 C3 Initial conditions
  (Explanans)
• F1 Fact- to- be- explained
• (Explanandum)

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Q Why does Gold expand when heated? (D-N)

• Answer
• P1 All metals expand when heated (law of
  nature)
• P2 Gold is a metal
• P3 A piece of gold is heated
• Conclusion The gold expanded

Explanans
Explanandum
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Q Why does Jones recover from streptococcus
infection? (I-S)

• Answer
• P1 The probability of recovery when penicillin
  is taken. (Probabilistic Law)
• P2 Jones takes penicillin
• ---------------------------------------
• Conclusion Jones recovered

Explanans
Explanandum
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• Conditions For Explanation
• 1) The explanandum is a logical consequence of
  the explanans.
• 2) The explanans contains at least one general
  law (probabilistic or strict)
• 3) The explanans has empirical content (not just
  true by definition).
• 4)The sentences in the explanans are true.

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Explanation Prediction

• One good consequence of the covering law model is
  that it also gives an account of prediction in
  science.
• P1 All metals expand when heated (law of
  nature)
• P2 Gold is a metal
• P3 A piece of gold is heated
• Conclusion Gold will expand when heated.

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(1) The Shadow and the Flagpole

• 37

15 Metre flagpole
37
20 Metre Shadow
A 15 metre flagpole casts a shadow of 20 metres
when the sun is 37 overhead.
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Problem (1) Symmetry

• Q Why is the shadow of the flag pole 20 metres
  long?
• (P1) Light travels in straight lines (Law of
  nature)
• (P2) Laws of Trigonometry
• (P3) The angle of elevation of the sun is 37
• (P4) The Flagpole is 15 metres high.
• Conclusion The shadow of the flag pole is 20
  metres long.

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Reversal!

• (P1) Light travels in straight lines
• (P2) Laws of Trigonometry
• (P3) The angle of elevation of the sun is 37.
• (P4) The shadow of the flag pole is 20 metres
  long.
• Conclusion The height of the Flagpole is 15
  metres!

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Problem (2) Irrelevance

• (P1) People who take birth control bills
  regularly dont become pregnant (Law)
• (P2) John has taken birth control pills for the
  past few years. (Initial Conditions)
• Conclusion John is not pregnant

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(3) Pre-emption

• (P1 ) Arsenic kills when ingested by human
  beings.
• (P2) John Doe ingests arsenic
• Conclusion John Doe Dies
• But John Doe was shot before the arsenic
• took affect.

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Explanation Causation

• The Problems associated with the covering law
  model suggest a link between explanation and
  causation.
• The shadow of the flagpole is not the cause of
  the height of the flagpole.
• Johns taking birth control pills is not the
  cause of him not getting pregnant.
• John Does ingesting arsenic is not the cause of
  his death.

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Causal Accounts of Explanation

• All explanations are causal explanations.
• All causal statements are counterfactual
  statements.
• Why did Jones die?
• Had Jones not driven when he was drunk he would
  not have prematurely died.
• Jones driving whilst drunk caused his premature
  death.
• Therefore, Jones died prematurely because he was
  drunk.
• (e.g. Lewis, David. (1986) Causal Explanation
  Philosophical Papers, vol. II, Oxford Uni Press. )

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Problem Causal Overdetermination Preemption

• What caused a certain car accident?
• The driver was drunk, visibility was bad, the
  corner was blind and the road was covered in ice.
  
• Had the driver not been drunk, he could still
  have crashed because of the ice, or the
  visibility.
• All of the factors comprising the causal history
  of the event are causally relevant. Lewis (1986)
• A full explanation will require an analysis of
  the full causal net.
• Salmon (1984) argues that a full account of the
  causal net, will require showing how events fit
  into the causal structure of the world.

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The Metaphysics of Explanation

• Which comes first - Explanation or Causation?
• Hempel - Explanation
• Salmon/Lewis - Causation.

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Bottom-Up

• Explanation
• Causation
• Determine the causal relations between
• particular events.
• Explanation the task of finding the
• causal mechanism responsible for the causal
• Sequence so as to explain the sequence of events.

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Top-Down

• Explanation
• Causation
• Causal concepts are derivative from explanatory
• concepts. (e.g. from concepts like laws of nature)

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Two metaphysical questions

• What is the link between explanation and
  causation?
• What is the link between laws of nature and
  scientific explanation?