Bengtsson does not squeeze the writers he studies into a straitjacket but identifies a common theme: what exists is personal or the product of the personal. This theme is consonant with Christian belief.  Theoretically, personalism does not rest on faith but it emerges within a Christian tradition. For some personalists the “distinction between Natural and Revealed theology in its old form thus vanishes. All theology is from one point of view revealed, and from another point of view it is natural.” [p. 56 quoting from Knudson.]  That idea is obviously debatable (in what sense is belief in the Trinity or the Incarnation natural?) ; it does, however, indicate the Christian influence in the personalist tradition.

If what exists is existentially intelligible – if the answer to Leibniz’ question as to why there is something rather than nothing is not simply that what exists simply happens, unintelligibly, to be – then the question as to the character of that intelligibility arises. Pantheism is one proposed answer; the impersonal self-explained Absolute another. In Christian reflection the proposed answer is the Trinitarian God – three persons in one nature or substance. The Latin ‘persona’– originally ‘a mask’ or role in theatre, then in Roman Law a ‘socially defined position’ – was borrowed, related to but not identical with the Greek ‘hypostasis’, to speak of the Trinity [one nature, three persons] and of Christ [one person, two natures]. Over centuries of theological reflection the notion of what it meant to be a person became clearer and was summarized in the West in Beothius’ definition: ‘person is an individual substance in a rational nature.’ [fn.4 p.131]. In his answer to the question as to whether or not it is suitable to use the name ‘person’ when writing of the divine persons, Aquinas wrote that ‘person signifies that which is  most perfect in nature, namely an existent in a rational nature (subsistens in rationali natura). [Sum.Theol. I.29.3] The members of the Trinity are distinct and are persons because each is a distinct existent in an intellectual or rational nature.

In his third chapter, ‘The personal absolute’ Bengtsson discusses later developments of the notion of person. Not alone for historians of philosophy but equally for philosophers of religion who would clarify their notion of God, that chapter is both very interesting and to some extent controversial as in the claim [underlined] that ‘…the God of personalism, while moral and rational…was distinctly more free, active, and willing than the Aristotelian actus purus into which the scholastic God tended to turn [p.133]. Later in the same chapter [p.137] he writes that ‘Jacobi insisted …that rationality implies personality… (so, quoting Jacobi) …if the world is to have a rational originator…then this being must be a personal being …There is no reason [Vernunft] except in personality [in Person], so since there is reason, there is a God and not merely a godhead [a divine, ein Göttliches]’.

Running through the book is reference to, and discussion of, Jacobi’s criticism of reason and his interpretation of nihilism that ‘were to become leading themes of modern philosophy. But none of the later philosophies determined by this problematic has done justice to Jacobi’s positive alternative – except personalism.’ [p.282]

In sum, Bengtsson’s discussion of these and other important questions makes his book well worth the considerable effort it requires to read it.