The Society of Bollandists lent me, for a liberal length of time, various rare books. I shall indeed be proud if my Appendix wins their approbation, since it deals with subject-matters and methods in which they are past-masters. Father Sticker’s pages on St. Catherine, in their _Acta Sanctorum_ (1752), are certainly not satisfactory; they are, however, quite untypical of the Bollandists’ best work, or even of their average performances. My obligations in my Psychological and Philosophical Parts First and Third are still more numerous and far more difficult to trace. Indeed it is precisely where these obligations are the most far-reaching that I can least measure them, since the influence of the books and persons concerned has become part of the texture of my own mind. But among the great religious spirits or stimulating thinkers of Classical and Patristic times, I am conscious of profound obligations to Plato generally; to Aristotle on two points; to St. Paul; to Plotinus; to Clement of Alexandria; and to St. Augustine. And the Areopagite Literature has necessarily been continuously in my mind. Among Mediaeval writers St. Thomas Aquinas has helped me greatly, in ways both direct and indirect; Eckhart has, with the help of Father H. S. Denifle’s investigations, furnished much food for reflection by his most instructive doctrinal excesses; and the extraordinarily deep and daring spirituality of Jacopone da Todi’s poetry has been studied with the greatest care. The Renaissance times have given me Cardinal Nicolas of Coes, whose great Dialogue _de Idiota_ has helped me in various ways. And in the early post-Reformation period I have carefully studied, and have been much influenced by, that many-sided, shrewdly wise book, St. Teresa’s Autobiography. Yet it is St. John of the Cross, that massively virile Contemplative, who has most deeply influenced me throughout this work. St. Catherine is, I think, more like him, in her ultimate spirit, than any other Saint or spiritual writer known to me; she is certainly far more like him than is St. Teresa. Later on, I have learnt much from Fénelon’s Latin writings concerning Pure Love, of 1710 and 1712; together with Abbé Gosselin’s admirably lucid _Analyse de la Controverse du Quiétisme_, 1820, and the Jesuit Father Deharbe’s solid and sober _die vollkommene Liebe Gottes_, 1856.