I read this book on Hilary Mantel's recommendation—by which I mean that she wrote about it, in one of the essays collected in A memoir of my former self. It should be obvious why it was of interest to her, as Keith Thomas's Religion and the decline of magic is a historical account of magical beliefs in the English Renaissance, the place and time in which Mantel's best known work is set. Her Cromwell trilogy is singularly well-crafted, in the way that it gives contemporary readers the sense that they are looking out at the world through the eyes of a man native to Tudor England. Understanding just what kind of an epistemological domain such people lived in was crucial to that effort. Her version of Thomas Cromwell is a pragmatist, but believes, as all intelligent, educated men did in his era, that religious ritual, astrology, natural magic and so on, are effective interventions in the world. What Thomas set out to do in his book, is to explain to a twentieth-century reader how beliefs that seem ludicrous to them, seemed natural to their ancestors.

For me, as someone engaged in fantasy worldbuilding and storytelling, it's very instructive to think about the ways that magic figures in real cultures and societies. As far as I can see, most fantasy writers think that this is something they can make up as they go along, and as they don't usually make any attempt to think themselves outside the paradigms they were born into, magic often becomes a species of science or technology. At the time Thomas is writing about, there was no science or technology—there was natural philosophy, and there was mechanics. This is more fundamental than a difference in terminology—we thought about the world in radically different ways then. Thomas sets out to comb through the historical record to find the evidence for this, and to offer his reader a detailed account of those differences.

Magic, the attempt to bring about a material outcome by the application of procedures we would not today see as causal, was something that could be found in every stratum of society. Many of the practices of the medieval church were magical, and after the Reformation there were many in England who tried to draw a line between superstitious Catholicism and rational Protestantism. Thomas points out the many survivals of magical practice and belief in the proliferating varieties of Protestant Christianity, as well as highlighting the increasing rationalism of European Catholicism. This is his approach throughout—a balanced account, that counters widespread misconceptions. The most widespread is that magical belief was a form of superstitious ignorance, waiting for the scientific worldview to come along and dispel it. He shows us both the rural folk-beliefs of the cunning-men and -women, and the educated, systematic practices of astrology and neo-Platonism, illustrating the ways that the Scientific Revolution arose from developments in alchemy, astrology, and other seemingly superstitious fields of knowledge.

The narrative is thematic, with sections on magic and religion, astrology, magical healing, prophecy, witchcraft, and other significant topics. His theme of the decline of magic is only explored in depth at the end, after he has presented a wealth of detailed evidence for its practice during the period in question (the text runs to 800 pages). To summarise it roughly, he believes that magic became less attractive as people came to believe in the power of human ingenuity and technical progress—but he notes the continued existence of newspaper astrology columns, and suggests that many people at the time of writing probably still harboured magical beliefs. This seems plausible as far as it goes. Religion and the decline of magic was published in 1970, and Thomas is cautious in many of his assertions, suggesting that the evidence had been insufficiently sifted. Much of it may have been examined more systematically in the succeeding 50 years—I don't know.

Overall, Thomas seems quite open-minded, and unwilling to patronise the beliefs of an earlier age which lacked the benefits of statistical analysis or the scientific method. He is very good at representing the ideological and epistemological milieu of the Tudor period, and showing the impossibility for its inhabitants of seeing beyond its paradigms. His account has dated in some respects, however. He often refers to 'primitive' religions and societies, as though the notion of progress were a given, whose technical connotations could not be separated from its cultural or social meanings. And he makes several references to magic and witchcraft 'in Africa', as though that enormous and uniquely diverse continent could be understood as a homogenous unity.

I don't just read books like this for 'research', although they clearly contribute to my understanding of the world, and my efforts to build imaginary ones. I read them for roughly the same pleasures that I derive from fiction—the joys of immersing myself in a world that is significantly different from the one in which I spend my daily life. As such, I come to them with the same appreciation of a well-turned sentence, and Thomas is a writer who understands the music of this particular mode of the English language. He writes, clearly, engagingly, and harmoniously, and his arguments flow smoothly through a very diverse series of discussions. I imagine that he had a general readership in mind, but I do get the impression that academic writing has tended to become more drily technical in the decades since this book was published. Religion and the decline of magic has taught me a great deal, and provoked a great many thoughts, but more to the point, it was a great pleasure to read it. 

Genuinely fascinating and insanely detailed account of magic in all its forms and the abandonment thereof. The specificity of the examples is stunning. One of those books that has fundamentally shifted my understanding of the periods and topics covered. 
The language is outdated in places but I can forgive that in a book from the 70s, though at times he makes generalisations that smack more of amateur anthropology than actual social history. The connections between folk magic in specific African tribes and that of 17th century England are sincerely interesting, but I'm not sure they're delved into enough to substantiate some of the conclusions drawn. 
Anyway I cried over the poor woman who was executed as a witch because of her mice 'familiars' called prettyman, littleman, and daynty. Also page 509 reshuffled my understanding of old theatre. This book is gonna stick with me.