The Structure of Scientific Thought

Science 240

Fall 2002

Notes on Popper

  1. It is easy to obtain confirmations for nearly every theory – if we look for confirmations.

  2. Confirmations should counts only if they are the result of risky predictions; that is to say, if unenlightened by the theory in question, we should have expected an event which was incompatible with the theory, an event which would have refuted the theory.

  3. Every good scientific theory is a prohibition:  the more a theory forbids the better it is.

  4. A theory which is not refutable by any conceivable event is non-scientific.  Irrefutability is not a virtue of a theory but a vice.

  5. Every genuine test of a theory is an attempt to falsify it, or to refute it.

    Testability is falsifiability;  some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks.

  6. Confirming evidence should not count except when it is the result of a genuine test of the theory.  This means that it can be presented as a serious but unsuccessful attempt to falsify the theory.

  7. Some genuinely testable theories, when found to be false, are still upheld by their admirers, for example by introducing ad hoc some auxiliary assumption, or by reinterpreting the theory ad hoc in such a way that it escapes refutation only at the price of destroying, or at least lowering, its scientific status.

    Note:  No rules or logic of acceptance.  If a theory passes a severe test, then we can only conclude that we have no reason yet to think that it is false. It might be true.

The Logic of Testing:

  1. Deduce a logical implication from the theory or hypothesis under test. This is a prediction about what data will be obtained under specified test conditions.  E.g We will see a shift in star light of  3 degrees 15 minutes. Under the conditions of the solar eclipse.

    This gives you a true conditional statement:

    If Einstein’s theory of GR is true, then the star light will be shifted by 3 degrees 15 minutes under the conditions of  the solar eclipse.

    Abbreviated:  If  T is true, then P under conditions TC.

  2. Obtain the test conditions.  Collect the Data.

  3. Either the Data match the prediction or they don’t.

    1. If the data don’t match – P is false.

      Use Modus Tollens to prove that the theory is false:

      If T, then P under conditions TC.

      Not (P under conditions TC)

      Therefore not T.

      On this model Newton’s theory was falsified in 1919 at the time of the solar eclipse.

      A good scientist should reject Newton’s theory.  She/he should invent a new theory  to explain the new data and explain all the old data that had been explained by Newton’s theory.

    2. If the data do match, you can not conclude that the theory is true.

      The following is a deductively invalid inference . It is not an inductive inference.  It is just bad.

      If T, then P under conditions TC.

      P under conditions TC.

      Therefore T.

      Popper: If the test was genuine and severe, the theory gets a big “plus” point.  Do another test.  Keep testing until you get a refutation or ….?

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