Lecture 5: 23rd September

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Lecture 5 23rd September
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• 1. Imagine an argument that you know to be
  deductively valid, but also to have an
  unjustified premise. As far as this argument is
  concerned, you should regard the conclusion as
  being
• d) Unjustified
• Beyonce is a dancer.
• All dancers are pot-heads.
• Thus, Beyonce is a pot-head.

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• 2. Imagine an argument that you know to be
  deductively valid, and to have justified
  premises. As far as this argument is concerned,
  you should regard the conclusion as being
• a) True
• All cats are mammals
• Jerry is a cat.
• Thus, this is a mammal.

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• 3. Imagine an argument you know to have all true
  premises but a false conclusion. Given no other
  information, you should regard the argument as
  being
• b) Invalid
• Validity An argument in which it is impossible
  that the premises be true and the conclusion
  false.
• All cats are mammals.
• Jerry is a cat.
• Jerry is a reptile.

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• 4. Imagine an argument you know to be valid but
  to have a false conclusion. Given no other
  information, you should regard the premises as
  being
• b) False
• Validity An argument in which it is impossible
  that the premises be true and the conclusion
  false.

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• 5. Is this argument valid?
• Today is Tuesday
• Thus, Today is Tuesday
• Yes. Circular arguments are valid.
• 6. Is this argument valid?
• Today is Tuesday or today is Wednesday
• Thus, today is Tuesday
• No. If its Wednesday, the premises will be true
  and the conclusion false.

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• 7. If there were any truth to the rumours about
  flying saucers, the Air Force would certainly
  deny it. So there must be something to the
  rumours because they certainly deny it.
• If there were any truth to the rumours about
  flying saucers, the Air Force would certainly
  deny it.
• The Air Force certainly deny it.
• Thus, there is truth to the rumours.
• If P then Q
• Q
• Thus, P
• Affirming the consequent. Invalid

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• You go on the ride only if you are over 5ft tall.
• Only if gives a necessary condition.
• If you go on the ride then you are over 5 ft
  tall.
• Going on the ride is sufficient for being over 5
  ft tall
• Being over 5ft tall is necessary for going on the
  ride.

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• 8. The supply of natural gas is unlikely to
  increase this year because the companies will
  increase the supply only if the price is allowed
  to rise, and the government will not act on their
  request for a price increase this year.
• Supply will increase only if the price rises.
• Price rising is a necessary condition for supply
  increasing
• If the supply increases, the price must have
  risen.
• Prices wont rise.
• Thus, supply wont increase
• If P then Q
• Not Q
• Thus, not P
• Denying the consequent. Valid.

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Evolution

• Hypothesis Plants and animals are
• the result of a process of natural selection
• Evolution will occur if and only if
• the following conditions are met
• 1. Variation. Different individuals have
• different features (morphologies, physiologies
  and behaviours). (Principle of heredity)
• 2. The variation is heritable offspring resemble
  parents. (Principle of variation)
• 3. Different variants leave different numbers of
  offspring. Scarce resources required. (Principle
  of differential fitness).

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Intelligent Design

• Hypothesis The plants and animals on Earth are
  the result of an Intelligent Designer.
• 1. Is this a scientific hypothesis?
• 2. If so, is it a good scientific hypothesis?
  i.e. is it supported by the evidence?
• Preview 1. Yes for our purposes.
• 2. No.

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Demarcating Science

• Logical Positivists Interested in separating
  science from pseudo-science. But they were really
  concerned with the elimination of metaphysics
  e.g. Nothing noths Heidegger.
• Verifiability A sentence is meaningful if only
  if there is a procedure that would determine
  whether it is true or false. Scientific
  Meaningful ( Verifiable).
• Ethical statements are not truth or false.

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Falsification and Testability

• Popper But sentences can be meaningful even if
  they are not testable. Such sentences are not
  scientific. So Popper developed falsificationism
  
• A sentence is scientific if and only if it is
  falsifiable. The more falsifiable, the better the
  theory.
• But sentences can be scientific even if not
  falsifiable e.g. there is a green swan.
• Thus, testability is better. A sentence is
  scientific if and only it is testable. The more
  testable, the better the theory.

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Digression Politics and Creationism

• If Creationism is not science, then it is
  religion, and it is unconstitutional to teach it
  in schools.
• First amendment "Congress shall make no law
  respecting an establishment of religion.or
  prohibiting the free exercise thereof
• The Butler Act (1925) banned the teaching of
  evolution in Tennessee.
• Scopes Monkey Trial (1925) John T. Scopes was
  prosecuted and convicted of teaching evolution in
  schools.
• We are not able to see how the prohibition of
  teaching the theory that man has descended from a
  lower order of animals gives preference to any
  religious establishment or mode of worship.
• Later cases were about over-turning laws that
  enforced the teaching of Creationism, rather than
  banning the teaching of evolution.

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• McLean vs. Arkansas 1982. The court decided that
  creationism is religion, not science. Science is
• 1. It is guided by natural law
• 2. It has to be explanatory by reference to
  natural law
• 3. It is testable against the empirical world
• 4. Its conclusions are tentative, i.e. are not
  necessarily the final word and
• 5. It is falsifiable.
• After such judgments, creationism turned into
  Intelligent Design.
• The Dover School Board case (2005). The US
  Federal Courts upheld that Intelligent Design
  was still not science.
• But Intelligent Design fits our 6 step model, so
  well consider it a science, in our loose
  understanding, as any model that purports to
  represent the world.

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Evolution and Testability

• Is evolution testable?
• No The theory of evolution does not predict
  that bears will evolve.
• Yes A rabbit from the pre-Cambrian age would
  refute evolution.
• Is Intelligent Design testable?
• No Intelligent design also does not predict
  that bears will evolve.
• Yes Are there features of species that would
  not be produced by an intelligent designer?

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Evidence Analogy

• Plants and animals are bred by humans to have
  useful traits artificial selection.
• Why couldnt plants and animals evolve by natural
  selection to have useful traits natural
  selection?
• This is a plausibility argument.
• Recall the Delorian example.

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Evidence Galapagos Finches

• Finches on islands distant from S America all
  resemble finches on the mainland.
• But they have beaks that fit the food they find
  on their respective islands.

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Evidence The Evolution of the Peppered Moth

• Originally, most peppered
• moths had light colouration
• to camouflage them against
• light coloured trees.
• Dark moths were caused by a single genetic
  mutation.
• During the Industrial Revolution, the trees
  became coated in soot, so only dark moths were
  camouflaged.
• By 1895, the mutation had a frequency of 98 in
  Manchester.

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Evidence Finch evolution

• In 1977 a drought reduced the population of one
  type of finch from 1000 to 200.
• The beaks of the next generation were bigger, and
  proportionately narrower and deeper, making them
  better for opening the last tough seeds.
• In 1983 there was a flood.
• The beaks of the next generation were smaller,
  which made them better for picking up the tiny
  seeds that covered the island.

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Finches Analysis

• 1. Real World. The real world area of interest is
  the origin of the shape and size of beaks of
  finches on the Galapagos Islands.
• 2. Model. The model is Darwins account of
  evolution by natural selection.
• 3. Prediction. Upon a dramatic change of the
  environment of the island, the size and shape of
  the beaks in the next generation should be
  different.
• 4. Data. Following both a flood and a drought,
  the beaks of the next generation were better
  adapted to find food in the new environment.
• 5. Negative evidence? No. The data agree with the
  prediction.
• 6. Were we likely to see different beak shapes
  even if Darwins model isnt right? Intelligent
  Design? No.

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Unintelligent Design

• The human spine, the appendix,
• short-sightedness, wisdom teeth
• and orthodontics, (physical pain?)

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Unintelligent design analysis

• Hypothesis The humans are the result of an
  intelligent designer.
• 1. Real World. The origin of humans.
• 2. Model. Humans have been created by an
  intelligent designer.
• 3. Prediction. Humans should be well-adapted to
  their environment.
• 4. Data. Humans have backs that are very poorly
  adapted for an upright posture.
• 5. Negative evidence? Yes. The data and
  prediction disagree.

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Unintelligent Design and Evolution Analysis

• 1. Real World. The origin of humans.
• 2. Model. Humans are the result of a process of
  natural selection.
• 3. Prediction. Humans should be well-adapted to
  their environment, but should have features that
  are remnants from the environment in which their
  ancestors lived.
• 4. Data. Humans have backs that are very poorly
  adapted for an upright posture, but well adapted
  for movement on all fours.
• 5. Negative evidence? No.
• 6. Positive evidence? Would we expect features
  that would be well adapted to the environment of
  apes if evolution were not correct? No.

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Big Bang Theory

• In the beginning there was nothing. Which
  exploded. Douglas Adams
• The universe began at a point of infinite density
  and temperature approximately 15 billion years
  ago.

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Steady State Theory

• New matter is continuously created, so the
  universe looks the same everywhere on a large
  scale as it always has and always will.
• Constant density would require roughly one
  hydrogen atom per cubic metre per billion years.
• Advocates have been motivated by a desire to
  eliminate any possible role for a creator.

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Background radiation

• Penzias and Wilson, two physicists working for
  Bell Telephone Laboratories built a receiver for
  communication experiments in 1965.
• They picked up an excess 3.5 Kelvin that they
  could not account for.
• This turned out to be the cosmic background
  radiation that the Big Bang theory predicts.

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Background Radiation Analysis

• 1. Real World. The origin of the universe.
• 2. Model. The universe began with a big bang.
• 3. Prediction. The universe should contain
  background radiation left over from the big bang.
• 4. Data. Radiation was detected by the receiver
  of Penzias and Wilson.
• 5. Negative evidence? No.
• 6. Positive evidence? Would we expect to see
  background radiation even if the big bang model
  were false? No, the steady state model does not
  predict such radiation.

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Anomalous Data

• The rate of expansion of the universe is
  increasing.
• 1. Real World. The origin of the universe.
• 2. Model. The universe began with a big bang.
• 3. Prediction. The rate of expansion of the
  universe should be slowing.
• 4. Data. The rate of expansion of the universe is
  increasing.
• 5. Negative evidence? Yes. Prediction and data
  disagree.

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New model

• Ad hoc modification Dark energy.
• 1. Real World. The origin of the universe.
• 2. Model. The universe began with a big bang and
  contains dark energy.
• 3. Prediction. The rate of expansion of the
  universe should be increasing.
• 4. Data. The rate of expansion of the universe is
  increasing.
• 5. Negative evidence? No. Prediction and data
  agree.
• 6. Positive evidence? Would we expect the rate of
  expansion of the universe to be increasing even
  if the model were false? No.