chapter  5
The grand design
Pages 27

Knowledge and certainty We have seen that Galileo and Descartes thought that mathematical laws of nature gave the truest and most objective account of the world; their view was that mathematical description was the ideal of philosophic inquiry. Descartes went further than Galileo because he believed that, in principle, empirical knowledge could be obtained by reasoning alone, and he attempted to present his own empirical knowledge as a deductive system in the confident expectation that ultimately all the laws of nature, and all particular events, would be logically deducible (and predictable) from self-evident premisses. Because that knowledge would be based solely on reason, and would therefore be independent of fallible sense experience, it would necessarily be true. Descartes's criterion of knowledge shows that he had inherited the Platonic and Aristotelian standard, namely that a claim to knowledge must be a claim to know for certain, beyond any possible doubt. Aristotle had asserted that only that which could not be otherwise should be rated as knowledge, or rather as what was called 'scientific knowledge'. 1 Unlike Plato, Aristotle had thought that observation, sense experience, could be a basis for this scientific knowledge but Descartes disagreed. 2 He argued that the only knowledge that could not be otherwise must be based on logical reasoning from self-evident premisses.