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Sir Karl Popper (1902-1994) was an insightful Austrian-born philosopher who had influence on science and politics.   

Sir Karl Popper (1902-1994) was an insightful Austrian-born philosopher who had influence on science and politics.   

In science Popper proposed a falsifiability criterion for the demarcation of science from psuedoscience as a result of his analysis of universal laws.  Universal laws have a logical structure which precludes certain existential statements: universal laws are a negation of an existential proposition.  Popper's example was that of the colour of swans.  The universal statement "all swans are white" implies the negative existential statement "no swans of a colour other than white exist".  To verify the negative existential we would need to trawl through the universe to ensure that no non-white swan existed anywhere in time or space.  Conversely if we saw just one black swan we could confirm the existential statement "black swans exist" and refute the universal "all swans are white".   

In science Popper proposed a falsifiability criterion for the demarcation of science from pseudoscience as a result of his analysis of universal laws.  Universal laws have a logical structure which precludes certain existential statements: universal laws are a negation of an existential proposition.  Popper's example was that of the colour of swans.  The universal statement "all swans are white" implies the negative existential statement "no swans of a colour other than white exist".  To verify the negative existential we would need to trawl through the universe to ensure that no non-white swan existed anywhere in time or space.  Conversely if we saw just one black swan we could confirm the existential statement "black swans exist" and refute the universal "all swans are white".   

Popper was uncompromising in his rejection of any attempt to take confirming instances as increasing the legitimacy, likelihood, reasonableness or probability of the universal statement.  No matter how many white swans you see you are no more able to assume that all swans are white than if you had seen just the one white swan.    The ease with which “confirming” instances can be found lead Popper to the conclusion that an attempted verification of a universal law is worse than useless: to be science universal laws must be capable of being put to the test, to be falsifiable.

Popper was uncompromising in his rejection of any attempt to take confirming instances as increasing the legitimacy, likelihood, reasonableness or probability of the universal statement.  No matter how many white swans you see you are no more able to assume that all swans are white than if you had seen just the one white swan.    The ease with which “confirming” instances can be found lead Popper to the conclusion that an attempted verification of a universal law is worse than useless: to be science universal laws must be capable of being put to the test, to be falsifiable.