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Lecture 5: 23rd September

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Beyonce is a dancer. All dancers are pot-heads. Thus, Beyonce is a pot-head. ... Being over 5ft tall is necessary for going on the ride. ... – PowerPoint PPT presentation

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Title: Lecture 5: 23rd September


1
Lecture 5 23rd September
2
  • 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.

3
  • 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.

4
  • 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.

5
  • 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.

6
  • 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.

7
  • 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

8
  • 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.

9
  • 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.

10
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).

11
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.

12
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.

13
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.

14
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.

15
  • 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.

16
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?

17
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.

18
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.

19
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.

20
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.

21
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.

22
Unintelligent Design
  • The human spine, the appendix,
  • short-sightedness, wisdom teeth
  • and orthodontics, (physical pain?)

23
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.

24
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.

25
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.

26
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.

27
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.

28
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.

29
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.

30
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.
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