Every so often an idea concealed for centuries from even the most dedicated historian of a discipline explodes quite without warning into new life to reconfigure an entire domain of that discipline. Strangely, some of the most momentous theological ideas of this kind emerge in the least accessible of sources. That is certainly true of the pivotal impact on recent Catholic and Anglican theologians of ‘integralist’ assaults on the idea of natura pura, which first sprang from Maurice Blondel's L'Action (1913), a forbiddingly dense work, and Henri de Lubac's Surnaturel (1946), a text which – at least in its original form – has still not found an English translator. But there is no work in twentieth-century philosophical theology in which one finds so sharp a disjunction between influence and accessibility as Erich Przywara's Analogia Entis (1932), a work that has been championed in key pronouncements by each of the last three popes and continues to exert a remarkable – if largely subterranean – influence on theologians today in ways that cut across many denominational and intellectual divides. It ranks as one of the most demanding and difficult texts in all of twentieth-century theology, yet its undeniable acuity and theological creativity have ensured that its foundational insight continues to generate important and clarifying debates among historical, doctrinal and philosophical theologians.

But what was that insight? To formulate it in its simplest terms, it is an attempt to explicate the God–world relation in a way that – in Przywara's view – avoided collapsing God into worldly sentiment (as, he insisted, Schleiermacher had done) or raising God to such an exalted degree of transcendence as to separate God from world altogether (as he accused Barth of doing). The solution, he insisted, was to understand the God–world relation in terms of an analogical bridge that both connects and separates divine and created reality, where the connection consists in both kinds of reality enjoying a mode of being, while the separation arises from the fact that every creaturely being's essence is distinct from of its existence whereas there is no real distinction to be drawn between what God is and that God exists. A crucial aspect of Przywara's thought is that the separation always trumps the connection, a principle neatly distilled in 1215 when the Fourth Lateran Council rejected Joachim of Fiore's trinitarian heresies by insisting that no similarity between God and creature could exceed the dissimilarity between them.

Even as crudely compressed a definition of the analogia entis as this might afford us a glimpse into just how contentious and unusual a theologian Przywara was. It is therefore especially gratifying to discover that Philip Gonzales's first book offers its readers such an incisive and perspicuous survey of Przywara's labyrinthine and astonishingly extensive corpus. It is a long book with a conceptually intricate architecture, but the basic shape is clear enough. The first part offers a thorough, appreciative (if occasionally uncritically so) and historically informed engagement with Pryzwara's Meisterwerk that positions it judiciously in the dynamic and chaotic currents of European philosophical theology entre-deux-guerres. The second half highlights the extraordinary fertility of the idea across a range of contemporary thinkers by drawing out the role it plays in the thought of William Desmond, David Bentley Hart, John Milbank and Cyril O'Regan (Gonzales is right to stress the denominational diversity of these thinkers, but he might also have noted that they are in fact close intellectual confrères, each of them being an important proponent of – or, at least, highly sympathetic towards – the constellation of ideas that makes up Radical Orthodoxy).

Gonzales uses the later work of the Carmelite mystic and phenomenologist Edith Stein to illuminate by contrast what he thinks Przywara gets right. Gonzales’ criticisms of Stein are difficult to ignore and mark a refreshing change from the tendency of much work on this neglected figure towards hagiography. A relatively sudden convert to Catholicism in 1921, Stein was a latecomer to theology and had no formal training in the subject at all (indeed her correspondence with Przyawara, from which she gained so much strength and encouragement in her own writings, was perhaps her only sustained intellectual relationship with a trained theologian). For all the energy she devoted to breaking from Husserlian phenomenology, her theological metaphysics bears the stamp of much of what she rejected: the lingering emphasis on the subject, the wariness of subsuming philosophical inquiry into theology and the insistence on treating ‘Christian’ philosophy as an exercise in the fulfilment of reason (a perfectum opus rationis). Each of these positions Przywara forcefully rejected, insisting as he did on treating theology as a single unified system encompassing all philosophical inquiry whose starting point was the study of God and not the study of the self's mode of access to God.

Gonzales does not attempt a full-throated defence of the analogia entis and this may disappoint those with well-grounded misgivings about the principle, or those seeking a more balanced appraisal of the many debates that have swirled around this contentious idea. Perhaps the book's only significant weakness is its author's tendency to assume that its readers will already be persuaded of the merits and coherence of the analogy of being. Why, for instance, was Cajetan – and the many who follow him on this point – mistaken to treat analogy as a semantic tool rather than a founding metaphysical principle? Why exactly was Barth's famous animus towards the analogy of being, which at one point in his life he considered the greatest obstacle to Catholicism, misplaced? Provocative and unfamiliar theological principles deserve careful dialectical treatment and their power can be obscured if articulated in an unduly declarative way.

At certain points the text might have benefited from a more ruthless editorial scalpel, bearing as it does some of the marks of the doctoral dissertation from which it emerged, especially in its slightly repetitious structural signposting and an overly cautious attitude of deference towards the major figures it engages that occasionally obscures the bold and imaginative constructive contributions the author seeks to advance. The author's search for an innovative nomenclature occasionally issues in clunky formulations that may puzzle uninitiated readers, as when in the introduction he labels Przywara's foundational contribution a ‘pleromatic analogical hermeneutic of non-identical repetition’, or proposes to advance an ‘analogical-apocalyptic metaphysics’.

Such cavils as these notwithstanding, there can be little doubt that Gonzales has produced a clarifying and often profoundly stimulating guide to Przywara's thought. The only English-language monograph of its subject to appear for many years, it will be essential reading for anyone with an interest in the many and various contentious ways in which analogy is deployed in modern theology.