In the course of the eighteenth century, understanding human cognitive life came to be construed as something to be explored in terms of the physiology of the sensory organs, the nerves, and the brain: a form of naturalization that effectively moved cognition out of the realm of philosophy as it had traditionally been understood. Bonnet's
Analytical Essay on the Faculties of the Soul
was at the forefront of these developments, and this is its first English translation. Drawing on his earlier work in natural history—he was the leading entomologist of his era—he approaches problems of the nature of the mind via the physiology and anatomy of the brain and sensory systems. His approach is one of 'reverse engineering', starting from an organic statue without faculties, and investigating how it would need to be modified to produce a human being.
Bonnet takes up a position that cuts across the standard understanding of the period as a clash between materialism and dualism. While his approach was rigorously naturalistic and physiological, this did not lead him to reject the notion of a soul. Instead, he argues that, in order to make sense of their sensory abilities, we need to attribute a soul to animals as well as human beings. At the same time, he argues that if personal immortality is to be possible, it can be conceived along the lines of insect metamorphosis, which shows how different biological forms can harbour a single identity.