A previously unpublished work by Michel Foucault, in which the French philosopher takes on sexuality among the early Christians, has been released in France, 34 years after his death.

Foucault published three volumes of the History of Sexuality, which explored the experience of sexuality in western society from the ancient Greeks to the modern day: The Will to Knowledge (1976), The Use of Pleasure and The Care of the Self (both 1984). The fourth volume was incomplete on his death in 1984 from an Aids-related illness.

Gallimard, which released Confessions of the Flesh last week, said the volume tackled the doctrines of Christianity between the 11th and 14th century, elaborating on Foucault’s belief that the majority of the rules and doctrines drew on the self-disciplines which Greek and Latin philosophers of antiquity had practised. The author had written a first draft of the work, according to the publisher, which called it “perhaps the heart of the enterprise, the part to which he attached enough importance to start on the project”.

Foucault specified in his will that he did not want his work to be published after his death. According to an essay by John Forrester in the book Foucault Now, he wrote: “Pas de publication posthume.”

“He would, it is said, admonish his friends: ‘Don’t pull the Max Brod-Kafka trick on me,’” wrote Forrester, adding that despite this, there has been “a continuous flow” of such works, “crescendoing” in 2004, the 20th anniversary of his death.

In an introduction, the philosopher Frédéric Gros lays out how the published volume of Confessions of the Flesh was drawn together from a handwritten manuscript of Foucault’s, and a typescript of the same work.

“The rightsholders of Michel Foucault considered that the time and the conditions had come to publish this major unreleased work,” he writes. “It is done now.”

The book, said Warwick University professor Stuart Elden, is in three parts. “The first discusses how the ancient notion of aphrodisia – a notion we might understand as pleasure – became replaced with the Christian notion of the flesh. That, in turn, precedes our modern understanding of sexuality. The second and third parts of the book discuss being a virgin and being married. These are the two key subjects that the church fathers are concerned with – the monk and the married man,” said the Foucault expert. “It is written in an austere style of textual analysis, without the kind of rhetorical flourishes that characterise some of his other work.”

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Elden, the author of Foucault’s Last Decade, said that in many ways the posthumously published volume was “the key to the whole History of Sexuality series”.

“Its initial title was La chair et le corps [The Flesh and the Body]. Foucault wrote much of a volume under this title. But he came to realise that crucial issues in the Christian tradition could be traced much further back. So through the late 1970s and early 1980s, which we can see in his lectures and other sources, he explored older and older historical material. This book is the result of this work,” said Elden.

Despite the volume’s seeming relevance to contemporary discussions around sexuality, Elden said that the late philosopher was “most often … concerned with the historical analysis of issues”.

“He spoke of his work as a ‘history of the present’, an examination of how we got to where we are, how what is currently taken for granted was made possible,” said Elden. “The issues he was concerned with – madness and mental illness, medicine and health, punishment, sexuality and so on – remain pressing issues today, and Foucault’s investigation of these issues, and perhaps especially the questions he asked about them, mean he continues to be a regular reference.”