Flesh in the Age of Reason by Roy Porter

of things, the imagination was prone to being deceived. In man and man alone, however, the intellect presided over the imagination, picking up and correcting its errors. Fed by such sense impressions, it also generated abstract concepts and formulated universals – God, infinity and eternity, and many other ideas far removed from sense and imagination.
    Animals were capable of a modicum of reasoning; in man, bycontrast, the intellectual powers were immense. Human reason could make inferences which far transcended mere sense perception; it could formulate axioms, unearth causes, handle mathematics, cultivate the arts, sciences and the ‘laws of political society’, and build wonderful machines. Above all, the rational mind could grasp the ineffable infinitude of God, and the reality of angels, heaven and hell. The reasoning power of brutes, by contrast, ‘will hardly seem greater than the drop of a bucket to the sea’.
    The distinction between the animal and the rational soul was thus not just one of degree but of kind – it was qualitative. The animal soul was material, the rational soul immaterial and immortal, divinely implanted. How then – a version of Descartes’s dilemma – did Willis envisage the links between the two kinds of soul in man? He endorsed the traditional Christian view of man’s tripartite nature: he possessed a body, an animal life shared with the brutes and, lastly, ‘spirit, by which is signified the rational soul, at first created by God, which being also immaterial, returns to God’. Man was thus midway between angels and brutes on the Chain of Being.
    The relationship between the two souls was complex. The animal soul pervaded the entire body, while the rational soul pertained exclusively to the head, dwelling within the brain as on a throne, just like a king in his palace. Like a monarch, the intellect did not need to attend personally to those functions served by the dutiful corporeal soul.
    The rational soul was nevertheless not aloof but plugged into the bodily economy. For its operation, it depended on the imagination, which was itself the end-point of the chain whereby sense impressions were carried to the nerves. Intellects in any case differed – was not one person cleverer than another? This was because of differences in their respective corporeal endowments and brain power. The intellect was thus in certain crucial ways contingent on the brain and hence the body.
    This championship of the rational soul shows how Willis, while a staunch advocate of the ‘new philosophy’, underwrote the Christian orthodoxies of the day: he came up with the physiological renderingof orthodox theological truths. Immaterial and immortal, the rational soul was ‘poured’ by God into the body. It also enjoyed, nevertheless, a well-defined place in empirical natural philosophy, explaining as it did features that would later be called psychological. Through authors like Willis, science and medicine would gradually replace churchmen as the accredited interpreters of the human.
    Just how widely read were Willis’s books is unclear, nor is it relevant. What is significant is that thinking such as his was becoming ensconced and diffused. Late-seventeenth-century élites were more or less aware that the old ways of talking about one’s body and its experiences – in terms of humours, ‘substantial forms’ and qualities – were on the way out, being challenged by new models, metaphors and focuses of attention (for instance, the nerves). As the fluids (humours) declined in prominence by contrast to the solids (organs), the guts, belly and bowels (those humoral containers) lost their ancient importance as referents for one’s self and its feelings, to be replaced in polite thinking by the head, the brain, and the nervous system. Thereafter, it was vulgar or plebeian to be preoccupied with such ‘low’ parts. Such shifts may have been reflected in speech. The old customs of declaring that one felt