Towards the beginning of Book 3, Lucretius starts his description of the soul. According to Epicurus, the soul is divided into two, an irrational part, which is coextensive with the body, and a rational part, the ‘mind’, which is located in the chest. This position is a relic from an earlier, non–philosophical tradition, and was adopted by several different philosophers. But Alexandrian doctors would soon correctly locate the mind in the head, and later Epicureans would have to defend an increasingly uncomfortable and out-of-date position.Footnote 1
Lucretius begins his report of Epicurus’ position as follows (3.136–42). I adapt Smith's translation to follow more closely Lucretius’ order of words and ideas.
Now I claim that the mind and spirit are held joined together and form one nature together, but it is the head, so to speak, and lord over the body that are the understanding which we call the mind and intelligence, and which, positioned in the middle region of the chest, stays there. For in this place throb terror and fear, hereabouts is melting joy: here therefore is the intelligence and the mind.
The argument, as Sanders showed,Footnote 2 is better than the commentators take it to be, and so is the humour.Footnote 3 Lucretius announces his topic, the two parts of the soul and their unity, and then immediately says sed caput ‘but the head …’. Someone unfamiliar with Epicurean philosophy notices nothing amiss, but someone who does know the basics of the doctrine in question is surprised: is Lucretius going to claim that the mind is in the head?!
No, but it takes him two and a half lines to get there. Absolute clarity about the mind's position only comes with pectoris in 3.140, and then he emphasizes the fixity of the position with situm … haeret. The mind, whatever the Alexandrian doctors might say, is definitely not going anywhere. The ‘real’ translation of 3.138–9 is ‘but the understanding, which we call the mind and intelligence, is like the head and controls the whole body’, but Lucretius has reversed the order of the sentence to put caput at its head. Epicurean readers will have been initially disconcerted, but then they smiled at the end of 3.140 when the joke became clear, and orthodoxy was maintained.
There is a follow–up joke at 3.150–1: cum cetera pars animai | per membra atque artus nulla nouitate cietur, literally ‘when the rest of the spirit throughout the limbs and frame is not stirred by any new sensation’, but also potentially ‘since the rest of the soul is not displaced throughout the various parts of the body by any innovation’ [sc. in doctrine]. Herophilus’ discovery of the nervous system was evidently not felt as a threat to the credibility of this part of Epicurean doctrine. nouitas may have a threatening tone.Footnote 4
There is another bit of doctrinal wit in the passage: the patterns of elision at 3.136 animum atque animam and 3.137 inter se atque unam naturam, both of which emphasize that the rational and irrational parts of the soul form a unity together.Footnote 5