Explanation and Realism

1
Explanation and Realism

• If two theories can differ with respect to their
  explanatory power, even though they both predict
  all the same phenomena, and if explanatory power
  is evidence for the truth of a theory, then the
  empirical equivalence of theories will not imply
  evidential equivalence (Ladyman, 196)

2
The battleground realists and constructive
empiricists on explanation

• What is a scientific explanation?
• Realists hold that the truth (or approximate
  truth) of a hypothesis is a necessary condition
  for it to be part of a genuine scientific
  explanation. That is why, for realists,
  explanations require more than empirical adequacy
  (what is empirical adequacy?)
• For the realists, inference to the best
  explanation (IBE) along with other
  super-empirical virtues show that empirical
  equivalence of theories does not imply evidential
  equivalence.

3
Scientific explanations

• The constructive empiricist must offer a critique
  of IBE if they are to succeed in arguing their
  case. Before we get to van Fraassens criticisms
  of IBE, let us consider what we look for in an
  explanation. Consider the following
• 1) The cup broke because it fell on the ceramic
  tiles.
• 2) The pressure of the gas rose because the
  volume was fixed and the temperature was
  increased.
• 3) The stone fell to Earth because its natural
  place is at the centre of the universe.
• 4) They are not answering the phone because they
  want to be left alone
• What are the common features in these examples?

4
Explanations

• 4) is an explanation by appealing to our
  background knowledge of how peoples behavior is
  related to their beliefs and desires.
• 3) is an example of an Aristotelian
  (teleological) explanation. That kind of
  explanation was rejected during the scientific
  revolution because it did not appeal to causation
• 1) 2) are both examples of causal explanations
  they attribute the structure of cause and effect
  to explain an event 2) is an example of a nomic
  explanation (appeal to laws of nature)

5
Scientific explanationsthe cover law model

• Indeed 2) would appear to be the kind of
  explanation of choice in the sciences explain
  the phenomena by discovering the laws of nature
  governing the phenomena.
• Explain the tides by appeal to law of
  gravitation, the mass of water in the oceans, and
  the mass and position of the moon.
• This is the cover law model. It was introduced by
  Carl Hempel. For him, to give a scientific
  explanation of an event is to show how it can be
  seen to follow from a law (or a set of laws)
  together with specific initial conditions.

6
Hempels deductive-nomological model

• Schematic for the deductive-nomological model (DN
  model)
• Laws l1, l2,
• Conditions C1, C2,
• _______________________________________
• Deductively entail explanadum O1, O2,
• Some terminology
• Explanadum what is being explained
• Explanans what does the explaining

7
Deductive-nomological model

• The DN model is also called the cover law model
  because the event explained is covered by some
  general law of nature.
• Logical conditions of the DN model (202)
• a) the explanans must deductively entail the
  explanadum
• b) the deduction must make essential use of
  general laws
• c) the explanans must have empirical content
• d) the sentences in the explananas are true

8
Deductive-nomological model

• a) requires that the explanadum must follow
  deductively from the explanans i.e. it is a
  deductively valid argument
• b) rules out the possibility of pseudo-scientific
  explanations, those that include laws to give the
  appearance of a scientific explanation
• c) requires that the laws and the initial
  conditions must be empirically testable
• d) ensures that the argument is deductively sound
  for a genuine scientific explanations appeal to
  true propositions

9
Deductive-nomological model

• Example why did the plant in the corner die?
• 1) no sunlight was reaching the plant in the
  dingy corner
• 2) sunlight is needed for photosynthesis
• 3) photosynthesis produces the carbohydrates
  necessary for survival
• Why is the above explanation a D-N explanation?

10
Problems with the DN model

• Two general kinds of problems
• 1) criticize the DN model as not necessary
• many explanations are perfectly acceptable
  without appeal to the DN model. So the DN model
  is too strict.
• E.g. Why did the Titanic sink?
• How would you defend the D-N model?
• The explanation in the sinking of the Titanic is
  only a sketch of an explanation. The relevant
  laws can in principle be discovered.

11
Difficulties with Hempels model

• 2) The D-N model is too liberal it includes
  explanations which are inadmissible. So the
  model isnt sufficient
• Defenders of the D-N model can account for
  objections under 1), but objections under 2) are
  much more difficult to answer
• Consider the following objections

12
Symmetry the thesis of structural identity

• Hempel the D-N model shows that explanation and
  predictions are flip sides of the same coin they
  have the same structure. The difference is that
  in explanation we already know that the
  conclusion of the argument (the explanadum) is
  true.
• Symmetry Information that allow us to predict a
  fact before we know it serves to explain it after
  its occurence.
• E.g. Newtonian mechanics predicted the return of
  Haleys comet in 1758, and once the comet has
  been observed, the same schema also explains why
  the comet returned when it did.

13
The problem with symmetry

• Suppose the goal post at University stadium cast
  a shadow 20 m long yesterday.
• How would you answer the question, why is the
  shadow 20 m long?
• The goal post is 15 m high, and suppose the angle
  of elevation is 37 degrees.
• The length is deduced from the height of the
  post, the angle of elevation, and laws of optics.
• This explanation fits the D-N model from laws,
  initial conditions, you explain the length of the
  shadow.

14
The problem with symmetry

• The problem with Hempels claim of symmetry is
  according to his account, the information about
  the length of the shadow and the angle of
  elevation is 37 degrees also explains the height
  of the post.
• Schematic of argument
• Laws opticslight travels in straight lines
• Conditions the shadow is 20 m, the angle of
  elevation is 37 degrees
• Conclusion the goal post is 15 m high
• If Hempel is right about symmetry, then it is the
  length of the shadow that caused the goal post to
  be 15 m high. But that explanation is
  counter-intuitive.

15
The problem with symmetry

• Hempels idea of structural identity in
  explanation and prediction is flawed because
  information that allow us to predict a fact
  before we know it may not serve to explain it
  after its occurrence.
• Hempels DN model does not respect the fact that
  explanations are asymmetrical If X explains Y,
  given the relevant laws and initial conditions,
  it is not true that Y will also explain X.

16
Other problems with the D-N model

• Irrelevance
• In the example below, the explanans fit the
  model, but one (or more) of the explanans is not
  a relevant explanatory factor.
• All salts dissolve in water
• Father OBrien put a sample of salt in holy water
• Therefore, the sample of salt dissolved
• What is wrong with this explanation?

17
Other problems

• Pre-emption an event that was going to happen
  for some reason happens earlier for another
  reason. For example
• Everyone who drinks a vat of Screetch gets really
  sick shortly thereafter
• Wong drank a vat of Screetch
• Therefore, Wong is really sick after the event.
• Whats wrong with this explanation?

18
Other problems

• Over-determination when there are more than one
  set of causal conditions at play, but each one is
  sufficient to bring it about. For example
• All people who do not have sex do not get
  pregnant
• John (who is a man) does not have sex
• Therefore, John did not get pregnant
• Note the objections of over-determination and
  pre-emption overlap one another

19
Summary of problems with D-N model

• The above counter-examples with regards to
  symmetry, irrelevance, pre-emption and
  over-determination show that the D-N model is not
  sufficient The logical conditions set out do not
  exclude explanations that are clearly not
  admissible.
• The moral behind these counter-examples is that
  the D-N model fails to respect features that are
  essential to a good explanation.

20
What about a causal account of explanation in
science?

• Given the problems with the D-N model, other
  accounts have been explored.
• Some put more emphases in the notion of
  causality. They argue that a causal account is
  not identical with the D-N account.
• The causal account would seem to respect, for
  instance, asymmetry of causes, and relevance of
  causal factors.
• The trouble with the causal account is that it
  raises the thorny issue of the metaphysics of
  causality.

21
Constructive Empiricist alternative

• How might a constructive empiricist respond to
  the question of exoplanation?
• van Fraassen seeks to avoid unnecessary
  metaphysical commitments. His approach is to
  argue that the explanatory power of a theory must
  take into consideration a pragmatic account.
• Consider the question, why did Bill buy that
  laptop?
• The answer would depend on the context and
  interest of the person asking the question.

22
Constructive Empiricism vs. Realism

• van Fraassens point the explanatory power of a
  theory is pragmatic and not because the answer is
  compelled by the way the world is.
• The realist, of course, claims the opposite, and
  the argument against anti-realism rests on the
  claim that the problem of under-determination
  (empirical equivalence is not identical with
  evidential equivalence) is solved by Inference to
  the best explanation type reasoning.

23
Problems with the DN model

• The second kind of problem uses counterexamples
  to show that the DN model is too liberal it
  includes explanations that are not genuine
  scientific explanations
• The problems can be grouped under irrelevance,
  preemption, overdetermination, and symmetry
  (203-204).
• Lets consider the problem of symmetry Hempel
  observed that according to his model that
  explanation and predictions are flip sides of the
  same coin they have the same structure
• The difference is that in explanation we already
  know that the conclusion of the argument (the
  explanadum) is true.

24
The problem with symmetry

• Suppose you notice that the goal post on
  Williston field today is casting a shadow 20 m
  long.
• How would you answer the question, why is the
  shadow 20 m long?
• The goal post is 15 m high, and the angle of
  elevation is 37 degrees.
• The length is deduced from the height of the
  post, the angle of elevation, and laws of optics

25
The problem with symmetry

• Suppose now we say that the goal post is 15 m
  high because the shadow is 20 m long and that the
  angle of elevation is 37 degrees.
• Schematic of argument
• Laws opticslight travels in straight lines
• Conditions the shadow is 20 m, the angle of
  elevation is 37 degrees
• Conclusion the goal post is 15 m high
• This explanation would also fit Hempels model
  but it is counter-intuitive. Why?
• The shadow does not cause the goal post to be 15
  m high.

26
The problem with symmetry

• Hempels DN model does not respect the fact that
  explanations are asymmetrical
• If X explains Y, given the relevant laws and
  initial conditions, it is not true that Y
  explains X.
• Hempels idea of structural identity in
  explanation and prediction is also flawed
  predictions and explanations part company as the
  flag pole example illustrates Information that
  allow us to predict a fact before we know it does
  not serve to explain it after we know it.