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Theory/Popper: not justifiable, but verifiable.
1. of any scientific theory one cannot know that it is true.
2. a scientific-empirical theory can contradict empirically observable facts.
3. a rational attitude is characterized by a critical attitude.
Theory: decide that there is an inter-subjectively ascertainable fact, which may, however, contradict the theory.
One theory has to contain one or more strictly universal statements (laws) e.g. "all bodies attract each other". General statement: E.g. "all items in my drawer are red": no strict general statement.
Definition basic statement: E.g. "at a certain time and in a certain place occurs this or that." A basic sentence may be in contradiction to the general statement, but cannot be derived originating. And expresses an intersubjectively observable fact.
General statement: a strictly universal statement is falsifiable if there is a possible basic statement, which contradicts it.
E.g. "in my kitchen on 11 June 1989, there is a green shrew". basic satement: "A green shrew does not exist".
A theory is only empirical scientific, if the class of its potential falsifiers is not empty.
It may turn out that basic statements were false, but one can also reject boundary conditions or additional hypotheses. Decisive: the assumption of a basic statement which is inconsistent with the statements contained in the test procedure, forces not to reject the central idea of a theory in general.
A new theory has to be able to solve the problems of the old theory. In addition, it must be able to solve the problems that the old could not solve. (New theory contains the old as a subset).
QuineVsPopper: this is a misconception: the new theory does not contain the old as a subset, but: E.g. also in everyday life, the theory of Newton is only an approximation.
Theory/Popper: new theories have excess content. - But then they should not be adapted ad hoc. - Lakatos: the excess content is created piece by piece, by extending the theories.
Objektive Erkenntnis Hamburg 1993