EPISTEMOLOGY give an account of their origin that closely resembles Aristotle’s When a man is born, his mind is like a blank sheet of paper, and as he develops towards the use of reason, concepts are written on the page The earliest concepts come from the senses: individual experiences leave behind memory, and memory builds up experience Some concepts are acquired from teaching or devised for a purpose; others arise naturally and spontaneously, and it is these that deserve the name ‘prolepsis’ (LS 39e) Concepts of this kind are common to all humans: disagreement arises only when they are applied to particular cases, as when the same action is described by one man as courageous and by another as lunatic (Epictetus 22 3) The Stoics developed a more elaborate classiWcation of mental states than ever the Epicureans did They wanted to propound an epistemology that would withstand sceptical challenge In addition to the two states of knowledge (episteme) and belief (doxa) that had been contrasted since Plato, they introduced a third state, cognition (katalepsis).5 The Stoics, Sextus Empiricus tells us, say there are three things connected to each other, knowledge and belief and located between them cognition Knowledge is cognition that is sound and Wrm and unchangeable by argument; belief is weak and false assent, and cognition is in between the two: it is assent to a cognitive appearance (M 150–1) A new element is here added to the deWnition of knowledge: knowledge is unchangeable by argument This seems a sound insight If I claim to know that p, I am claiming, among other things, that no one is going to (rightly) argue me out of believing that p This is unlike the case where I believe that p but am open to conviction that not-p This latter is what is meant by saying that belief is weak assent It is also (possibly) false: there is nothing absurd in saying ‘X believes that p, but it is false that p’ as there is in saying ‘X knows that p, but it is false that p’ But the most interesting point in this passage is the deWnition of cognition in terms of cognitive appearance (phantasia kataleptike) ‘Appearance’ is a broad term, including not only what appears to the senses but candidates for belief of other kinds Cognitions, likewise, may result from the senses or from reason (D.L 52) An appearance is not the This translation is now standard, being used by Long and Sedley (LS 254) and Frede (CHHP 296 V.) I use it with reluctance, since the word ‘cognition’ is associated with much confusion in modern philosophy of mind 170