Lecture 1 Logical positivism

1
Lecture 1Logical positivism
2
The basic historical facts

• Logical positivism started as a philosophical
  movement in Austria (the Vienna Circle) and
  Germany (the Berlin Circle) in the mid-1920s.
• The main representatives Rudolf Carnap, Moritz
  Schlick, Carl Gustav Hempel, Hans Hahn, Herbert
  Feigl, Philipp Frank, Hans Reichenbach, Richard
  von Mises, etc.
• With the rise of Nazism in the 1930s, most
  logical positivists emigrated to the United
  States, and exerted an extremely strong influence
  on American Philosophy.

3
The philosophical background

• Empiricism-rationalism debate
• What is the main source of knowledge observation
  (Locke, Berkeley, Hume), or reason (Descartes,
  Spinoza, Leibniz)?
• The third way Kant
• Kant was basically an empiricist, but he thought
  that science gave us some knowledge that is so
  certain that it cannot be based just on
  observation.
• Examples Euclidean geometry, arithmetic, the
  principle of causality, Newtons laws of motion
• Kants problem Some knowledge in science cannot
  be based just on observation, but on the other
  hand, observation is the only way to know
  anything about the external world.
• His solution the doctrine of the synthetic a
  priori.

4
Analytic - synthetic, a priori a posteriori

• Analytic syntheticAnalytic statements true
  by virtue of their meaning (Examples All
  bachelors are unmarried, Tomorrow it will
  either rain or not rain) Synthetic statements
  not analytic (Tomorrow it will rain, All
  Lingnan students are unmarried)
• A priori a posterioriA priori statements
  their truth can be established without
  observation (Examples All bachelors are
  unmarried, Tomorrow it will either rain or not
  rain) A posteriori statements their truth
  cannot be established without observation
  (Tomorrow it will rain, All Lingnan students
  are unmarried)

5
Kants table
6
Speculative philosophy after Kant

• Of the three categories of statements, the most
  interesting is synthetic a priori, because only
  it contains general, necessary and deep truths.
  The other two are either trivial and
  uninteresting (analytic), or relating to
  knowledge that has no necessity and generality
  (synthetic a posteriori).
• Since Kant used philosophical arguments to
  explain our knowledge of synthetic a priori, some
  philosophers after him (Hegel and Schelling)
  tried to develop comprehensive systems of
  knowledge by using pure thinking (speculation).
• They didnt call it synthetic a priori but they
  were definitely trying to discover some deep
  truths about the world without making
  observations.

7
The Elimination of Metaphysics

• Logical positivists detested speculative
  philosophy or metaphysics, as they called it.
  They regarded statements made by Hegel, Schelling
  and Heidegger as not just false, but meaningless.
• The truth can be known only by (1) analyzing
  meanings or (2) by observation. All else is
  nonsense!
• If we take in our hand any volume of divinity or
  school metaphysics, for instance let us ask,
  "Does it contain any abstract reasoning
  concerning quantity or number?" No. "Does it
  contain any experimental reasoning concerning
  matter of fact and existence?" No. Commit it then
  to the flames for it can contain nothing but
  sophistry and illusion. (Hume)
• Another cell in Kants table became empty.

8
The logical positivists table
9
The principle of verifiability

• Some statements are meaningless, although they
  appear to have some meaning.
• The fire that passed into crystal is its own
  melting, self-burning, in which the crystal
  becomes a volcano. The volcanoes should not be
  understood too mechanically, but as a storm with
  earthquake that happens beneath the earth.
• What does that statement mean?
• Or the following Nothing nothings. (Heidegger)
• Logical positivists tried to find a way to
  distinguish real statements from (meaningless)
  pseudo-statements. They were looking for a
  criterion of demarcation.
• Their solution the principle of verifiability A
  statement is meaningful only if there is a
  possible experience (observation) that would show
  that the statement is true.

10
Why the principle of verifiability?

• The idea behind the principle if you know what
  the statement mean, you know what would make it
  true. But if you know what would make it true,
  you know how the world would look if the
  statement was true. But if you know how the world
  would look if the statement was true, then you
  know what observations you would make if you were
  there, and if the statement was true.
• Two senses of the principle strong and weak.
• Strong verifiability it must be possible to
  prove that the statement is true.
• Weak verifiability it must be possible to show
  that the statement is probably true.
• The weak version is preferable. (Scientific laws
  speak about infinitely many objects and cannot be
  verified in the strong sense.)

11
Some problems with the principle of verifiability

• Some statements seem to be perfectly meaningful
  but it is not at all clear how they could be
  verified by observation.
• Example Murder is wrong, The world will still
  exist even after all conscious life disappears
• What about the principle of verifiability itself?
  Is it verifiable or not? If yes, how? If not,
  then it is meaningless because it is not an
  analytic statement.
• The principle of verifiability was supposed to
  divide all non-analytic sentences in two groups
  (a) meaningless (metaphysics and other nonsense),
  and (b) meaningful (science in the first place,
  but also ordinary common-sense statements etc.).
• But it was not successful. On strong
  interpretation, it did eliminate metaphysics,
  but it excluded some scientific statements too.
• On weak interpretation, it preserved science, but
  some metaphysical statements crept in as well.

12
Humes problem of induction

• How do we verify a universal generalization?
  (Scientific laws are often universal
  generalizations.)
• We observe many swans, and on that basis we
  conclude that (S) All swans are white. Is S
  really verified by these observations?
• Obviously, despite all the observations of white
  swans, S may still be false.
• The usual answer is that the observations do not
  prove S, but they certainly make it probably true
  (weak verification).
• But Humes argument was precisely that we have no
  reason whatsoever to think that S is even
  probably true!
• If all observed swans were white, How can we
  logically justify our expectation that the next
  swan will also be white?
• Hume argued that we cannot. Logical positivists
  tried to show that we can. Their attempt to build
  a system of inductive logic were not very
  convincing. Humes problem remained unsolved.

13
Why not jump out of the window?

• Answer I will fall and hurt myself. But how do I
  know that I will fall?
• Answer Law of gravitation. But how do I know
  that the law of gravitation is true?
• Answer Verified by observation (All objects
  without support fall toward the surface of the
  earth.) But in fact observation only tells me
  that in the past all observed unsupported objects
  fell. How do I know that I will fall if I jump
  now?
• Answer The fact that all unsupported objects
  always fell in the past shows that this is a law
  of nature. Otherwise, it would not have always
  happened. But I dont see that. It is a logical
  fallacy to conclude that an observed regularity
  will continue into the future. Why shouldnt I
  jump?
• Answer Well, then jump, you, moron!

14
Science and verifiability

• There is an inferential gap between premises
  about observation and the conclusion (scientific
  law).
• An argument is obviously deductively invalid.
  Humes challenge is to find an inductive or
  probabilistic justification that could make the
  argument reasonable.
• Logical positivists (especially Carnap) tried to
  develop inductive logic that would serve this
  purpose, but they were not very successful.
• Scientific laws are often regarded as having some
  kind of necessity (Unsupported objects must
  fall, Every biological organism must die). But
  it turns out that we are not only unable to
  explain their necessity. We cannot even show that
  they are true! We cannot verify them.