1 Logical Positivism

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    September 8, 2004 Philosophy of science 1

    Lecture 1

    Logical positivism

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    September 8, 2004 Philosophy of science 2

    The basic historical facts

    Logical positivism started as a philosophicalmovement in Austria (the Vienna Circle) andGermany (the Berlin Circle) in the mid-1920s.

    The main representatives: Rudolf Carnap, MoritzSchlick, Carl Gustav Hempel, Hans Hahn, HerbertFeigl, Philipp Frank, Hans Reichenbach, Richard vonMises, etc.

    With the rise of Nazism in the 1930s, most logicalpositivists emigrated to the United States, and

    exerted an extremely strong influence on AmericanPhilosophy.

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    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 sciencegave 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 theonly way to know anything about the external world.

    His solution: the doctrine of the synthetic a priori.

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    Analytic - synthetic, a priori a posteriori

    1. Analyticsynthetic

    Analytic statements = true by virtue of their meaning(Examples: All bachelors are unmarried, Tomorrow itwill either rain or not rain)Synthetic statements = not analytic (Tomorrow it willrain, All Lingnan students are unmarried)

    2. A prioria posterioriA priori statements = their truth can be established withoutobservation (Examples: All bachelors are unmarried,Tomorrow it will either rain or not rain)

    A posteriori statements = their truth cannot be establishedwithout observation (Tomorrow it will rain, AllLingnan students are unmarried)

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    Kants table

    A priori A posteriori

    Analytic All bachelors are unmarried.

    Synthetic

    Every event has a cause.

    7 + 5 = 12

    Euclidean geometryThe law of conservation of matter

    Newtons laws of motion

    Tomorrow it will rain.

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    Speculative philosophy after Kant

    Of the three categories of statements, the most interesting is

    synthetic a priori, because only it contains general, necessaryand deep truths. The other two are either trivial anduninteresting (analytic), or relating to knowledge that has nonecessity and generality (synthetic a posteriori).

    Since Kant used philosophical arguments to explain ourknowledge of synthetic a priori, some philosophers after him(Hegel and Schelling) tried to develop comprehensivesystems of knowledge by using pure thinking (speculation).

    They didnt call it synthetic a priori but they were definitelytrying to discover some deep truths about the world withoutmaking observations.

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    The Elimination of Metaphysics

    Logical positivists detested speculative philosophy ormetaphysics, as they called it. They regarded statementsmade by Hegel, Schelling and Heidegger as not just false, butmeaningless.

    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 schoolmetaphysics, for instance; let us ask, "Does it contain anyabstract reasoning concerning quantity or number?" No."Does it contain any experimental reasoning concerningmatter 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.

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    The logical positivists table

    A priori A posteriori

    Analytic

    All bachelors are unmarried.

    7 + 5 = 12

    Euclidean geometry (pure)

    Synthetic

    Tomorrow it will rain.

    Every event has a cause.

    Newtons laws of motion

    Euclidean geometry (applied)

    The law of conservation of matter

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    September 8, 2004 Philosophy of science 9

    The principle of verifiability

    Some statements are meaningless, although they appear tohave some meaning.

    The fire that passed into crystal is its own melting, self-burning, in which the crystal becomes a volcano. Thevolcanoes should not be understood too mechanically, but asa 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 realstatements from (meaningless) pseudo-statements. Theywere looking for a criterion of demarcation.

    Their solution: the principle of verifiability: A statement ismeaningful only if there is a possible experience(observation) that would show that the statement is true.

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    Why the principle of verifiability?

    The idea behind the principle: if you know what thestatement mean, you know what would make it true. But if

    you know what would make it true, you know how theworld would look if the statement was true. But if youknow how the world would look if the statement was true,then you know what observations you would make if youwere there, and if the statement was true.

    Two senses of the principle: strong and weak.

    Strong verifiability: it must be possible toprove that thestatement is true.

    Weak verifiability: it must be possible to show that the

    statement isprobably true. The weak version is preferable. (Scientific laws speak about

    infinitely many objects and cannot be verified in the strongsense.)

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    Some problems with the principle of verifiability

    Some statements seem to be perfectly meaningful but it is not at allclear how they could be verified by observation.

    Example: Murder is wrong, The world will still exist even after allconscious life disappears

    What about the principle of verifiability itself? Is it verifiable or not? Ifyes, how? If not, then it is meaningless because it is not an analyticstatement.

    The principle of verifiability was supposed to divide all non-analyticsentences in two groups: (a) meaningless (metaphysics and othernonsense), and (b) meaningful (science in the first place, but alsoordinary common-sense statements etc.).

    But it was not successful. On strong interpretation, it did eliminatemetaphysics, but it excluded some scientific statements too.

    On weak interpretation, it preserved science, but some metaphysicalstatements crept in as well.

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    Humes problem of induction

    How do we verify a universal generalization? (Scientific laws are oftenuniversal generalizations.)

    We observe many swans, and on that basis we conclude that (S)All swansare 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 notprove S, but they certainly

    make itprobably 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 ourexpectation 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.

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    Why not jump out of the window?

    Answer: I will fall and hurt myself. But how do I know that Iwill fall?

    Answer: Law of gravitation. But how do I know that the law ofgravitation is true?

    Answer: Verified by observation (All objects without supportfall toward the surface of the earth.) But in fact observation

    only tells me that in the past all observed unsupported objectsfell. How do I know that I will fall if I jump now?

    Answer: The fact that all unsupported objects always fell in thepast shows that this is a law of nature. Otherwise, it would nothave always happened. But I dont see that. It is a logical fallacyto conclude that an observed regularity will continue into thefuture. Why shouldnt I jump?

    Answer: Well, then jump, you, moron!

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    Science and verifiability

    There is an inferential gap between premises aboutobservation and the conclusion (scientific law).

    An argument is obviously deductively invalid. Humeschallenge is to find an inductive or probabilistic

    justification that could make the argument reasonable.

    Logical positivists (especially Carnap) tried to developinductive logic that would serve this purpose, but theywere not very successful.

    Scientific laws are often regarded as having some kind ofnecessity (Unsupported objects mustfall, Every

    biological organism mustdie). But it turns out that weare not only unable to explain their necessity. We cannoteven show that they are true! We cannot verify them.