Lecture 9 Scientific Explanation

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Lecture 9Scientific Explanation
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Is explanation reduction to the familiar?

• A natural suggestion explaining means to reduce
  something strange (and not understood) to
  something familiar.
• But sometimes we explain phenomenon A by
  phenomenon B, although B is actually less
  familiar than A.
• Example Olbers paradox.
• Why is the sky dark at night?
• The obvious answer Because there is no sun is
  incorrect.
• The fact is that from certain plausible
  assumptions (e.g., that the universe is not very
  small, that stars or galaxies are uniformly
  distributed in space, etc.), we should expect
  that the night sky would not look different from
  the sky during the day.
• The sky at night should not be dark!

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Olbers paradox
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Hempels covering law model of explanation

• The explanation consists of the explanandum (what
  has to be explained) and the explanans (what is
  explaining it).
• Four basic conditions for explanation
• The explanation must be an argument where the
  explanandum deductively follows from the
  explanans (in the D-N, or deductive nomological
  explanation), or where the explanandum is made
  highly probable by the explanans (in the I-S, or
  inductive statistical explanation).
• The explanans must have empirical content, be
  independently testable (to avoid
  pseudo-explanations, like dormitive power,
  entelechy).
• The explanans must contain at least one general
  law (hence the name, the covering law model).
• The explanans must be true.

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What is a law?

• Law is not any universal generalization.
• Some generalizations are accidental
  generalizations, like All coins in my pocket are
  HK dollars.
• How to distinguish between accidental and
  law-like generalizations? The latter support
  counterfactual statements, while the former do
  not.
• For example, All metals expand when heated
  supports the counterfactual statement If x had
  been a metal, it would have expanded when
  heated.
• But All coins in my pocket are HK dollars does
  not support the counterfactual statement If x
  had been a coin in my pocket, it would have been
  a HK dollar.

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Problems with Hempels model

• One can criticize Hempel in two ways
• That his conditions are not sufficient, i.e. that
  something can fail to be an explanation, despite
  satisfying all the conditions.
• That his conditions are not necessary, i.e., that
  something can be an explanation, despite not
  satisfying some of his conditions.
• Both lines of criticisms have been tried, and
  numerous counterexamples were proposed.
• Hempels general idea that explanations are
  always arguments was also attacked. It led to his
  defending the structural identity of
  explanation and prediction, which was a special
  source of problems.

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Not sufficient

• In some cases, all the conditions are satisfied
  but the explanans is irrelevant for the
  explanandum. For example
• 1. No man taking contraceptive pills becomes
  pregnant.2. Peter has been taking contraceptive
  pills.Therefore, Peter has not become pregnant.
• The explanans (1 2) is true, has empirical
  content, contains a general law, and deductively
  entails the explanandum, yet it is not an
  explanation.
• Another example
• 1. Everyone who takes a pound of arsenic dies.2.
  Peter took a pound of arsenic.Therefore, Peter
  died.
• But assume Peter was killed before the poison
  took effect. Again, no explanation although all
  the conditions satisfied.

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Not sufficient (2)

• Sometimes, all the conditions are satisfied and
  the explanans is relevant but there is no
  explanation. Take first case C
• 1. Laws of optics (light rays are straight
  lines).2. Position of the sun and the height of
  the flagpole.Therefore, the length of the
  flagpoles shadow.
• Good explanation! But now consider D
• 1. Laws of optics (light rays are straight
  lines).2. Position of the sun and the length of
  the shadow.Therefore, the height of the
  flagpole.
• Well, this does not look like an acceptable
  explanation at all. Surely, we cannot explain the
  height of the flagpole by the length of its
  shadow! (But Hempels conditions are met.)

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Not sufficient (3)

• Two more examples where all the conditions are
  satisfied, the explanans is relevant for the
  explanandum, but does not explain it
• 1. Laws of meteorology.2. A drop in the
  barometer.Therefore, the storm is coming.
• We do not think that a barometer drop explains
  the storm.
• 1. Laws of celestial mechanics (motions of sun,
  planets)2. Present positions and speeds of sun,
  earth and moon.Therefore, the time of the next
  eclipse of the sun.
• Good explanation! But if using (1) and (2) we
  derive the time of the past eclipse of the sun
  (which is easily done), in that case we do not
  see this derivation (F) as an explanation of the
  past eclipse.

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Not necessary (condition 1)

• Let us consider Hempels condition (1), that the
  explanandum has to follow deductively from the
  explanans (D-N) or to be made highly probable by
  it (I-S).
• The famous counter-example due to Michael
  Scriven
• Paresis is caused only by untreated syphilis, but
  most people with untreated syphilis do not get
  paresis. John has paresis. Therefore, Johns
  paresis is explained by his untreated syphilis,
  although it cannot be predicted from it.
• Hempel argued that if most syphilis patients do
  not get paresis, then Johns paresis is not
  explained by his having syphilis.
• According to him, to explain X is to show that,
  given the facts in the explanans, X was to be
  expected.

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Not necessary (condition 3)

• Are the laws really indispensable for
  explanation? Some examples seem to show that this
  central requirement of Hempels covering-law
  model may not be necessary. Consider example H
• An ink stain on the carpet is explained by my
  knocking over an ink bottle.
• The idea here is that we explain a situation (ink
  stain) by an event, without postulating any laws
  that cover the two.
• If the example is not convincing, more persuasive
  illustrations can come from history (the
  assassination of the arch-duke Ferdinand
  explaining the beginning of World War 1) or
  biology (the meteorite explaining the extinction
  of dinosaurs).

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How to improve on Hempels model

• The first option is to try to patch up the model,
  especially the defects of sufficiency. In fact,
  all the examples A-F can be subsumed under the
  model if there is an additional requirement of
  causal relationship between the explanans and the
  explanandum.
• There is a causal influence from the flagpole to
  the shadow (C), but not the other way around (D),
  yes from earlier to later (F) but not from later
  to earlier (F), not from arsenic to death (B),
  nor from contraceptive pill to non-pregnancy (A),
  nor from barometer to storm (E).
• Hempel and positivists did not like to invoke
  causality because the concept was unclear. It is
  not particularly clear today, but some
  philosophers prefer to analyze explanation in
  terms of causality, without the covering law part.

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Pragmatics of explanation

• Van Fraassen emphasizes the importance of
  context. Every explanation is an answer to a
  Why-question, but every question has the form
  of Why this rather that? To understand the
  request for explanation we have to know what the
  contrast class is.
• When gangster Willie Sutton was asked by the
  judge Why did you rob the banks?, he answered
  Because this is where the money is.
• He misunderstood (or pretended to misunderstand)
  the judges question. The question was not Why
  did you rob the banks rather than libraries?. It
  was Why did you rob the banks rather than
  getting a job? The contrast class defines the
  Why-question.
• Different requests for explanation in the
  question Why did Adam eat the apple?, depending
  on what is emphasized (Adam, eat, or apple).

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Contrast class

• Take the paresis example (G). Is syphilis the
  explanation of Johns paresis? Well, it depends
  on what is the contrast class.
• If the question is why John, rather than someone
  without syphilis, got paresis, then syphilis is
  the explanation.
• But if the question is why John, rather than
  someone else with syphilis, got paresis, then
  syphilis is not the explanation.
• In the flagpole and the shadow example (C), we
  can actually imagine a context in which the
  length of the shadow would explain the height of
  the flagpole.
• For example, a flagpole of a given height is
  chosen just because at a crucial time of the day
  it gives a shadow of the same length as a
  romantically important person who stood at that
  place in a memorable moment in the past.