Dr Grazia Mangano Ragazzi is an independent researcher with an international academic formation in theology. She brings to this very accomplished study of St Catherine of Siena (c.1347–1380) the kind of passionate engagement that characterised the saint herself. The quip, that mysticism begins with mist and ends in schism, is not applicable to Catherine, and from Mangano Ragazzi's book we can see why in scholarly detail. Catherine's works are available in modern English translation by Suzanne Noffke, and now we also have an up-to-date and reliable point of entry in English into the life and thought of a most remarkable saint with the focus on a single, pivotal term.

This term is ‘discrezione’, translated as ‘discretion’, and it is taken as basically synonymous with ‘prudence’. Mangano Ragazzi makes clear from the outset that today's widespread understanding of these two English terms has been so devalued that far from signifying an attitude of courageous witness to the truth they have largely come to mean timidity if not outright connivance in sin. The notion of ‘verbicide’, the murder of a word or at least of its original or nobler meaning, is adapted from C.S.Lewis and used vigorously. Discretion is also understood as a wider and more complex term than discernment.

Minimal but sufficient biographical information is provided, more attention being paid to the still vexed, although of paramount importance, questions of Catherine's ‘authorship’ of the writings attributed to her: the Dialogue, the Letters and the Prayers. The research involved is subtle and substantial. Whether engaged in textual criticism or in analysing the meaning and role of discretion (Parts I and II), these three sets of writings are examined in turn and considered as a whole. The extent to which Catherine could read and write remains unsettled, and we cannot go back to anything written by Catherine herself. The degree of interpolation and interpretation attributable to her disciples and amanuenses has to be a constant concern, yet Mangano Ragazzi repeatedly and for good reasons argues in favour of reliability and coherence. We can get a sense of the divergences among scholars simply by noticing that when it comes to Letter 273 (the dramatic account of an execution), Fawtier rejected its authenticity whilst Dupré Theseider thought there was nothing imaginable that is more authentically Catherinian.

The fourth and last Part offers a synthesis by considering discretion as the bond between mysticism and morality. In it, a concluding and illuminating definition is offered. For Catherine, discretion may be defined as knowledge and love of the truth in action, namely that knowledge and love of the truth (which is God) that leads concretely to virtuous action. It is the practice of discretion that leads us to dwell in divine grace, to unify the human faculties of memory, intellect and will, and to advance in charity. Not surprisingly then, the New Testament passage most frequently quoted in Catherine's writings is John 14:6 where Christ reveals himself as the way, the truth and the life. Mangano Ragazzi might have given a more prolonged and systematic discussion of Catherine's knowledge and use of the bible. The Letters of Catherine, some 382 in total, can be read as evidence of her intense desire to discover the truth and apply it to real life (she was very Dominican in this). There are letters to popes, cardinals, religious, sovereigns, politicians, relatives, friends, acquaintances and some to people she had never met.

In essence, Mangano Ragazzi proposes three fundamental aspects of discretion for Catherine: its central place in her writings, its originality, and the role it plays in integrating the unity of her teaching. The argued-for centrality needs and receives sustained attention based on chapters 9–11 of the Dialogue and Letter 213 (to another mantellata, Daniella d'Orvieto) yet is not limited to those fundamental texts. The mention of originality needs to be assessed in terms of the survey offered in Part III of this book, which consists of a comparison in historical perspective. Here are traced the origins of discretion for Catherine: from the tradition of discretio and prudence to the synthesis of Aquinas and the reflections by some of Catherine's contemporaries. Comparison with St Thomas Aquinas is of course necessary although not straightforward, and Thomas Deman is quoted approvingly as saying that Aquinas entrusts prudence with the task of perpetuating the constant and venerable tradition that discretion had carried through to him. It is improbable that this doctrinal richness resulted from Catherine's direct access to the texts, and so its mediation must have come mainly through her way of life and contacts. Spiritual affinities must not be ruled out, and Catherine believed that in Aquinas (‘il glorioso Tomaso’) divine Truth involved supernatural light and knowledge infused by grace. Thus Aquinas learned more through prayer than through human study.

In terms of the influence on Catherine of the Dominican milieu in particular, attention should be paid to Domenico Cavalca's The Mirror of the Cross, a small book written in the vernacular and with a wide dissemination. Mangano Ragazzi maintains, however, that Cavalca could not have been more than a minor source of Catherine's exposition of discretion. Something Kenelm Foster wrote in his insightful introduction to I, Catherine (1980, in collaboration with Mary John Ronayne) is apposite; in a certain sense, all theology worthy of the name is in tendency ‘mystical’. As for mystics in the more usual sense of the term, whether their contact with God will give rise to clearly articulated doctrine will depend, humanly speaking, on their natural gifts and circumstances. For Mangano Ragazzi, Catherine's thought seems to depend on a unique form of inspiration, expressed in all her writings and giving them a unified character.

According to Giuliana Cavallini, and how great a debt is owed to her scholarship, there is perhaps no virtue which is so characteristic of Catherine as discretion. It is a characteristic feature of Catherine because of the prominence she attributes to it and the great extent to which she practised it. Mangano Ragazzi has now enabled us to see this. One can only conclude that, in Catherine, Christian mysticism, doctrinal truth and sustained action interpenetrated to an extraordinary and saintly degree.