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So what if Karl Popper changed his mind about induction early in his career ("Popper 'falsified' old ideas", THES, July 25)? What is important is the innovative anti-inductivist argument that he subsequently created.

Your report makes the common mistake of implying that the idea "all swans are white" can be proven false by the sighting of a black swan.

A decision as to whether or not a theory has been falsified is always a matter of judgement, and judgement is potentially flawed.

Falsification is not a route to certain knowledge of what is not true; there is no proof of falsehood in the empirical realm You also conflate Popper's early work on falsification with his critique of induction. On page 1 of Objective Knowledge, he said he had "reached the solution (to the problem of induction) in 19 or thereabouts". He did not claim to have done so in 1919.

Joanna Swann
King's College London