But what certainty is available outside mathematics and pure philosophy? Can Descartes maintain that the truths of empirical science, including his own discoveries, have the certainty of demonstrations? In the exuberance of youth, his answer was yes. But even an intellectual ego as robust as the Cartesian proved subject to the erosion of certainties from long experience of life. The source of trouble was argument “from effects to causes”; very frequently in Descartes’ science he infers the truth of a theory from its ability to explain phenomena. But surely this cannot be a demonstrative
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