This is an original work of intellectual history. Kruger employs Derrida's category of "spectral presence" (taken from the book Specters of Marx, (first French edition 1993), in which the public debt and globalisation are seen as a "spectral presence" of an absent Marx) to understand the relationship between Jews, a homogeneous and separate minority (66), and Christians, the majority group in the Middle Ages.
Kruger employs the concept of spectral presence to develop a psychoanalytic approach to law and society. This analysis is useful, since it gives Derrida's argument broader application. Similarly, Cohen and Dahan, two scholars in the field of the relations between Jews and Catholics in the Middle Ages, employ the category of the theological Jew, which is not an image of real Jews. But the idea that the living realities of Jews and Christians are experienced through the constructions of fantasy and ideology rather than solely in an existential realm (xxi) is grounded in the notion that legislation is not simply a factual and material matter. Legislation, as Pierre Legendre stresses, is the manifestation of the emblems of one society, i.e. the way to manifest what you cannot say without contradiction ("emblem" is a more unconscious notion than "symbol"). Kruger reflects the influence of Derrida when he suggests, albeit implicitly, that the constructions of fantasy and ideology are in some way arbitrary and purely subjective (10). This is not Legendre's approach. Instead, Legendre argues that the construction of law via the Lacanian Third (in the Middle Ages, the Apostolic See of Rome) is necessary and it is also the groundwork of a civilisation. So, one might agree with Kruger's methodology and with some of his conclusions, but one might also disagree with his exaggerated estimation of sexual character and representation in the normative relations between medieval Jews and Christians (74, 76). Conclusions of this type are visible in the discussion about gender in saint Peter Damien (92) and Peter Alfonsi and Inghetto Contardo on merchant identity (145, 151), and sexuality in Guibert of Nogent (41 and passim). Kruger's argument is not explicit enough on this theme, so I cannot develop it (but see the discussion on pages 69 and 73, which presents arguments I believe are unsound).
Embodiment and disembodiment are the working categories in this book, and they are employed to show how the sense of identity of the members of a community unites them against the "other". So, Kruger presents Jewish individual body as part of a whole body of Jewry, in a contested holistic relation marked by the "vicious" Jewish body and a religion identified with bodylines. The central argument is that medieval Christian anxiety about the Jews is marked by a lack of attention to any communal or social Jewish life. The more materialistic, economical and social, i.e. Marxist, way to think about this history is quite outside the scope of the work.
Kruger's idea that in Christian thought the Jew is a presence- absence is quite right and fruitful. Christian Law follows Jewish Law and it is the transformation or "spectral inheritance" (11) of Jewish Law--the true Israel against the untrue and actual Israel of Jews. It is therefore necessary for Christian normative systems to acknowledge the presence of Jewish Law as the Father, but it is "impossible" to live with a Father that does not die, and this Father is the Jew who refuses to become Christian (the killing of the Jew is at least a phantasmatical "necessity" in Christian history). The moment of Christ's incarnation rewrites all of history: Christianity can teach to Jews the best way to understand the Talmud, in that the Apostolic See is the true Israel, i.e. the legal authorised interpreter of Holy History (on the Tortosa disputation and this "jurisdiction", see page 194). The real presence of the Jew is necessary to link the Old and the New Testament, but his real presence is a negativity because it is absence of conversion: it is a psychoanalytical and anthropological feature that the authors of anti-Jewish pamphlets are converted Jews.
Kruger associates the intensification of the real relationship between Christians and Jews with the intensification of violent relationships between the two communities: this is an issue of the phantasm of confusion, in that to affirm the difference in the similarity may evoke the unconscious fear of the total identification (for simultaneous attraction and aversion, see page 134). The pamphlets written by Catholics against Jews have the same violence as the pamphlets written by Jews against Catholics (and the rationalist Maimonides is perhaps more virulent than the mystical Nachman). Sometimes these pamphlets have the same arguments, with an inversion of the good and bad characters--the Papal injunction about wet nurses stressed on pages 89-90 was employed (evidently, inverted) some years before by Maimonides in his Mishne Torah from the Talmud in the text of XIIth century (see my paper La nascita della riflessione normativa francescana nel XIII secolo e l'influenza della tradizione ebraica: una ipotesi, in L. A. De Boni, R. H. Pich, editors, A recepcao do pensamento greco-romano arabe e judaico pelo Ocidente medieval, Porto Alegre 2004, 520-521). This is not only matter of a spectral Jew, it is also matter of a spectral Christian; or it is something more complex : this is a question that Kruger's work does not address.
Kruger analyses the matter of the naturality of being-Jews: a conversion is a matter of will, but the "vicious" body of the Jew cannot be "converted" to a Christian (not-vicious) body. Kruger suggests that a "quasi-racial" definition of Jewishness can be identified in this context, but this is an open question: the emblematical and symbolical--i.e., religious--approach to Jews is not immediately compatible with this "quasi-racial" approach. The pamphlets of anti-Jewish literature are very rich in suggestions to answer this question. Kruger approaches the work of Rupert of Deutz and Peter Alfonsi--a quite original writer--using his "spectral" view. Similarly, he uses this analysis to examine the disputations of Paris (1240), Barcelona (1263) and Tortosa (1413-14). This pamphleteer production makes a sort of determination of dogmatic meanings--in the meaning of "dogmatic anthropology" by Legendre, and these are also Kruger's words: "Christianity is not just one alternative to other systems of beliefs, it effects a universal reorganisation of human life" (3, 39). This dogmatic work is to remind Christian society that their conversion is the mark of the "impossibility" of the conversion of every Jew, in that also the Scriptures testify that in the day of the Last Judgement Jews must be present. Or in Peter Alfonsi's fictional dialogue, "a residue of Jewish identity is ineffaceably inscribed within Peter's celebration of his own embracing" (123) of catholic faith. Finally, "the convert remains a convert" (162).
In the end, Kruger's "complex rationale" (5) presents a true contradiction: Jewish peoples must be present by their absence, the Jews' conversion must operate through their unworking heirs. In some way, also saint Peter Damien's pamphlet against sodomitic monks is the mark of the necessity of the conversion of Christian people (especially, religious men) and at the same time the testimony of the impossibility of a full conversion in this actual word--the Fall makes our body a "vicious" body. This is a theological matter, not a "quasi-racial" matter as Kruger suggests (167); this is an anthropological matter, but not of a biological or physiological anthropology. As the sodomitic monk must be "limited" to avoid his threaten to Christian truths, the Jewish presence cannot threaten Christian truths--"the feared incursion of the perverse" (96): the Fall is the mark of actual human nature, but not of blessed human nature. To believe in this central feature of the Fall for anthropology is to believe in the objective nature of perversion: to stress that "as Christianity replaces Judaism, prayer replaces sex" (109) is a sign of a different approach. Nevertheless, I agree with Kruger that, as he ends his book, the spectral Jew haunts the project of a Christian Europe. Finally, it is worth remembering that although during the Middle Ages there was a "real" Muslim threat against Christian Europe, the embodiment and disembodiment of Jews was not quite comparable to that of Muslims, as some passages of Kruger's book may suggest (51, 99).