EPISTEMOLOGY Aristotle on Science and Illusion In epistemology, as in other matters, Aristotle’s agenda was set by Plato He accepted Plato’s distinction between the senses and the intellect, and attached great importance to it, often attacking earlier thinkers, such as Empedocles and Democritus, for failing to appreciate the distinction between sensation and thought (e.g Metaph G 5.1009b14 V.) With the Theaetetus in mind, he addressed once again the Protagorean question of the reliability and fallibility of the senses Finally, he took over and developed the Platonic catalogue of diVerent intellectual states; and set out criteria for the attainment of the highest such state, namely scientiWc knowledge Plato frequently emphasized the unstable and confusing nature of senseexperience For instance, in the tenth book of the Republic he wrote, ‘Things look crooked when seen in water and straight when seen out of it; things can look both concave and convex because colours mislead the eye; and all kinds of similar confusion are manifest in our souls’ (602c–d) He contrasted this with the constancy of the results of the calculations and measurements carried out by the reasoning part of the soul Aristotle considers the epistemic status of the senses in the course of defending the principle of contradiction against Protagorean arguments in Metaphysics C (5 1009b1 V.) The problem arises from the occurrence of conXicting sense-impressions We have these four propositions (1) (2) (3) (4) Sense says that p Sense says that not-p What Sense says is true Not both p and not-p This is an inconsistent quartet: any three of the propositions can be used to prove the falsity of the fourth This possibility is used in diVerent ways by diVerent protagonists in to the debate that Aristotle is addressing Democritus and Plato, followed by sceptics ancient and modern, accept (1), (2), and (4) as showing the falsity of (3) Aristotle’s Protagoreans accept (1), (2), and (3) as showing the falsity of (4) In modern times some philosophers have sought to defend (3) and (4) by qualifying (1) and (2) and introducing the notion of sense-data Sense, according to these philosophers, does not really say that the stick is straight and that the stick is not straight; it 161