On the basis of positivist epistemology lays the empirical observation (verification criteria), which takes shape with the experimental method. The self-obvious recognition of the positive character of experience as the exclusive criterion of truth is the characteristic feature of positivism, throughout all the forms of Greek and Western philosophical tradition. Karl Popper, in the 1930’s, went against the positivist ratification and rejected the inductive method. To find a way out of the dead-end of inductivism, Popper presented an alternative method of inference, which replaces the principle of verification with the principle of falsification. The epistemological method of Popper, based on conjectures and formulations, is also known as falsificationism, or method of trial-and-error. In this method, science does not start from observations in order to proceed through the way of inductive inferences, according to the inductivist position. By contrast to the positivist view, it starts from certain conjectural hypotheses, which are being put to the test of empirical testing and scientists try to reformulate them, keeping a critical stance in the process and experimenting with alternative hypotheses. So, in place of the inductive method, Popper proposes the deductive reasoning (from the general to the specific) through the process of falsification (refutation) of a hypothesis (or a conjecture).
A scientific theory which survives after a substantial amount of critical examinations and empirical tests can be accepted on a temporary basis and not permanently, until the time comes of some future test that will over-throw it. In other words, for Popper no theory is verifiable, it may only have a high degree of empirical strength, which implies that all scientific theories are in principle falsifiable. Added to that, there are many theories that continue to be accepted despite the fact that their validity has already been seriously challenged. Newtonian mechanics was an example of such theories. Newton’s theory had an extraordinary agreement with observation and experiment at the time of its appearance (1687) until 1900. But in the first twenty years of the 20th century, its validity was challenged from the new viewpoint of relativist mechanics, without however been abandoned. A similar situation exists for the Euclidean geometry which is considered to be valid for the Earth but no so in the Universe.
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