Soul Machine: The Invention of the Modern Mind. By George Makari. W.W. Norton; 656 pages; $39.95; 672 pages; £24.99.

ABOUT a century and a half ago, an American railway worker named Phineas Gage was setting an explosive charge near Cavendish, Vermont. While he was tamping down the charge with an iron rod, it went off and sent the rod through his head. Gage miraculously survived—or least part of him did. But contemporaries thought that his personality had changed; where once he had been well-behaved, now he was downright antisocial. The incident raised questions about what constitutes the self and to what extent it is influenced by the body.

Although Phineas Gage is cited in medical and psychological literature as one of the earliest known cases of brain damage and personality change, the debate about what makes people human had, by then, already been going on for centuries. In “Soul Machine” George Makari, a psychiatry professor at Weill Cornell Medical College, presents an electrifying narrative of the intellectual disputes that gave rise to the Western conception of the mind. 

His book focuses on the period between 1640 and 1815. As wars and religious conflicts plagued Europe, philosophers and scientists sparred with each other over whether a human’s inner self was an immortal and divine essence, or merely a fallible natural object. Out of confusion and combat eventually grew the idea of the modern mind, which was “part soul and part machine”.

Mr Makari’s highly engaging story begins with René Descartes, who was born in 1596. Ever since Greek philosophy had merged with Christianity, the soul had been regarded as the “unifying link between nature, man and God”, Mr Makari writes. By the 17th century, however, Christendom was in crisis and many found it hard to reconcile the notion of an incorporeal soul with a mechanical world that was increasingly understood as made up of matter. Descartes tried to satisfy the demand of sceptical naturalists by severely narrowing the concept of the soul to a “thing that thinks”, yet that was separate from the body. The French philosopher thus breathed new life into the Christian belief in an immortal soul, which may go some way towards explaining why he dedicated his “Meditations on First Philosophy” to the “most wise and illustrious the Dean and Doctors of the Sacred Faculty of Theology in Paris”.

At the other end of the spectrum stood Thomas Hobbes, born eight years before Descartes, who thought there was no such thing as “immaterial substance”. In his view the soul, rather than being rational and Godlike, was “material, prone to illness and errors”. The disparate views on the nature of the “thing that thinks” was to have monumental implications. And it demonstrates the importance of Mr Makari’s narrative as more than just an intellectual exercise. After Hobbes concluded that men were controlled by animal feelings that inevitably produced conflict, his proposed solution was to hand over power to an absolute monarch. John Locke, by contrast, envisioned a mind whose rationality was bounded but yet encompassed reason and free will—a notion that would help give birth to political liberalism.

Mr Makari’s historical account of the modern mind is a doorstop of a book. To the author’s credit, he makes a subject that some may find hard to digest more easily accessible by adding colour to the many dead European thinkers around whom “Soul Machine” is centred. Descartes is described as “vain, brilliant and reclusive”, Locke is “sagacious” and Hobbes is, he writes, considered part of a “growing band of rebels”.

“Soul Machine” is an ambitious work. It covers political turmoil, religious heterodoxy and scientific discovery—often within the same paragraph—and boasts a formidable cast of characters. Any reader who is not thoroughly schooled in modern Western history may find Mr Makari’s detailed account confusing. Although fundamental questions about the self have yet to be resolved, human beings today, as Mr Makari concludes, tend not to spend most of their waking hours dwelling on their existence, but instead simply embrace the belief that most people possess the capacity to think, choose and love as “modern hybrids of soul and machine”.