According to a widely circulated story, German Idealism developed, almost by necessity, as a way of augmenting Kant's transcendental turn, reaching Schelling's Naturphilosophie and Hegel's absolute idealism via Reinhold's Elementarphilosophie and Fichte's Wissenschaftslehre. Contrasting with this is a different and more complex story, little known beyond the circle of specialists. It was promoted from the 1960s on by Dieter Henrich who focused on neglected aspects of the early beginnings of the German idealists, such as Fichte's original insights into the nature of self-consciousness (Henrich Reference Henrich1967), Schelling's early theological and Platonist explorations (Henrich Reference Henrich1971), and especially Hölderlin's crucial influence on the formation of Hegel's Jena system (1971). What emerged was an explanation of the rise of German Idealism as a reaction to and appropriation of Kant's and Plato's philosophies, set against the Protestant theology of the time. As Henrich put it in his essay ‘Hegel und Hölderlin’ (in Henrich 1971), what constituted the original problem of the German idealists were two concepts, unio and synthesis, ‘the basic notions of the Platonist tradition and Kant's thought’.

While Henrich's approach to German Idealism has greatly inspired international scholarship, his account of Hölderlin's influence on Hegel is better known in the German-speaking literature. According to Henrich, ‘Hegel owed his friend much more than the latter could ever owe the former’ (Henrich Reference Franz2010: 11). Hölderlin's pre-Fichtean ideas had a Platonist source and concerned a philosophy of love or union, partly prefigured in Hemsterhuis, Herder and Schiller, a philosophy for which Henrich coined the term Vereinigungsphilosophie. Hölderlin had identified two essential and opposing principles, or tendencies, of human existence, the principle of union or association and the principle of separation, dissociation or individuation. To solve the conflict between these principles he postulated a meta-principle of their union: the union of union and its opposition. The similarity to Hegel's ‘identity of identity and non-identity’ is striking. This meta-union could not be reached without facing conflicts first, indeed facing the principle of conflict (separation). It therefore had to be carried out over time, becoming ‘a force, not to be understood in a static way, but only as a movement through opposing poles. A force turning into a principle of history’ (Henrich Reference Franz2010: 17).

Henrich's concept of Vereinigungsphilosophie was taken up by his pupils, for instance by Gerhard Kurz, Panajotis Kondylis and Christoph Jamme, who made it the foundation of a research programme. In his new book, titled Tübinger Platonismus, Michael Franz argues that this programme is a questionable one. To be sure, Franz agrees with Henrich and his school that Hölderlin was a major influence on Hegel. And he certainly does not deny that Hölderlin sought a mediation between Plato and Kant. But he aims to show, as he argues against Kurz in particular, that

In Franz's view, the fuzzy concept of Vereinigungsphilosophie is ill-suited to capture this doctrine and, more generally, to help us understand the peculiarities of the Platonist framework which was so essential to the rise of German Idealism. The aim of Tübinger Platonismus is systematic: the painstaking reconstruction of this framework, focusing on the early philosophical exchange between Hölderlin, Schelling and Hegel (Fichte is a more secondary figure in this scheme). But since this Platonist framework emerged through a complex interplay of philosophical and theological currents to which the three protagonists were exposed in the context of their studies at the Tübinger Stift, Franz chooses a method that is, to a considerable extent, historical. His detailed knowledge of this context, paired with an admirable ability to trace the often unpredictable development and ramifications of ideas over time, make for a fascinating read, undermining the false dichotomy between ‘historical’ and ‘systematic’ approaches.

Tübinger Platonismus is divided into three parts—‘Vorgeschichte’ (‘pre-history’), ‘Hölderlin’ and ‘Schelling und Hegel’. Each part contains three essays. The first part deals with the understanding of Plato and neo-Platonism in Germany in the 18^th century and particularly in Tübingen. Its first essay discusses the particular blend of humanism and Protestant theology in Tübingen through which Schelling and Hölderlin became acquainted with Plato's ideas (Franz has investigated this issue with respect to Schelling at great length in a previous book, Schellings Tübinger Platon-Studien (Reference Franz1996)). Franz points here also to one of their theology professors, Johann Friedrich Flatt (1759–1821), an astute critic of Kant's treatment of rational theology and his practical ‘proof’ of the existence of God. Flatt partly anticipated the objections Hegel were to make against Kant and Jacobi in Glauben und Wissen (Reference Franz1802). The next two essays deal with similar topics. One concerns the (partly critical) treatment of neo-Platonism in the influential histories of philosophy authored by Jakob Brucker (1696–1770), Christoph Meiners (1747–1810) and Georg Gustav Fülleborn (1769–1803) in the 18^th century, the other discusses the status of Patristic philosophy in Tübingen around 1790. These essays demonstrate that an adequate understanding of the origins of German Idealism requires that we take into account the incredibly rich and sophisticated philosophical and theological culture in Germany, and especially in Tübingen.

The second part is dedicated to Hölderlin, with essays on his early Plato studies, on the Platonism of his prefaces to Hyperion, and on his friendship and philosophical relation with Schelling. These essays belong to the highlights of the book. I focus on the second essay, ‘Hölderlin's Platonismus. Das Weltbild der “exzentrischen Bahn” in den Hyperion-Reden’ (95–122), originally published in 1997. Like Henrich, Franz does not think that Hölderlin's contribution to German Idealism was merely ‘aesthetic’, that he merely urged his friends Hegel and Schelling to consider beauty as an ideal of perfection (as Dilthey was the first to argue in Das Erlebnis und die Dichtung, Reference Dilthey1906). Whereas aesthetics belonged for Hölderlin to the ‘the highest of things’ (cf. the letter to his brother in March 1796), the philosophical concept of beauty he aimed to investigate belonged to the ontological foundations of the world (95f.). From a metaphysical point of view we need to start with the latter, not the former. The key concept here is that of the ‘eccentric orbit’ or ‘eccentric course’ (‘exzentrische Bahn’), which occurs in all three versions of Hyperion, and especially in the forewords to the first two versions (1794, 1795). The eccentric course which the protagonist Hyperion follows in the novel in an exemplary way (‘from childhood to perfection’) is an irreversible course between two states, the first a state of utter simplicity or unity, the second a state of perfection. But in fact Hölderlin distinguishes three states: simplicity/unity, perfection, and the eccentric path connecting the two. This suggests a triadic and dynamic scheme, applicable to the development of every individual, but also to the history of the whole species. It is also an eschatological scheme, for it offers a prospect of salvation from our current predicament. According to the penultimate Hyperion-preface (1795), the triadic scheme starts with a ‘sacred unity’. We are now in the intermediary state of the eccentric path, which is a state of dissociation (‘Entzweiung’), of ‘the rift between our self and the world’. It is also a state in which we strive to overcome this rift by reaching the third state, harmony beyond all opposition, i.e., perfection or beauty.

As Franz points out in his essay on Schelling and Hölderlin, Schelling was talking about a similar ‘rift’ at the same time, in Vom Ich als Princip der Philosophie (1795), also searching for a way to overcome it by employing a triadic scheme (142ff.). But Hölderlin's triadic scheme differed in crucial aspects from Schelling's. Unlike Schelling he did not believe that the scheme is of the form 1 – 2 – 1, i.e., that we can return to the initial stage, which is forever lost. Our fall is irreversible and the structure of the last stage must reflect this progress; this gives us 1 – 2 – 3, i.e., 1 – 2 – (1 + 2). Hölderlin describes this stage as εν διαϕεϱον εαυτ $$\[--><$>{\tf="Pi1"\char111}\hskip-4.3pt\vskip 2pt{\scale85%.}\hskip2.5pt<$><!--$$ , ‘the One differentiated within itself’, a concept of great importance in Hegel's later work. Also, for Hölderlin the final stage cannot be forced by human action or reason. Final union and salvation are only given through grace, as ‘beauty’ which is already ‘there’. For ‘a new realm is waiting for us, where beauty is reigning as queen’ (Hyperion, penultimate preface).

How are we to make sense of the expression ‘eccentric orbit’? Franz denies that it refers to Kepler's elliptical orbit, although ‘eccentric’ did have this contemporary use, for instance in Kant's The Only Possible Proof (1763). Man's life is neither elliptical nor periodical. Neither does Hölderlin refer, in his view, to the path of something which has temporarily deviated from the regular course of nature, but might return back to it, which is how ‘eccentric’ was employed in a dialogue by Christoph Gottfried Bardili (1761–1808), a lecturer at the Tübinger Stift. The third contemporary meaning of the term was ‘meteoric’ and also drops out (99f.).

What follows is a captivating reconstruction of a fourth possible meaning of ‘exzentrische Bahn’, which reads like a detective story. We noted the unity-dissociation-unity structure of Hölderlin's triadic eschatology. Its historical sources include Luther, who also spoke about the ‘realm of beauty’, and Joachim of Fiore. But Franz argues that the genuinely philosophical source is to be found in Plato's metaphysics, especially its ‘esoteric doctrine’, as worked out by the Tübingen school around Konrad Gaiser and Hans Joachim Krämer, a school largely ignored by Henrich. This is the doctrine of the μόνας (unity) and the $$\[--><$>\ralpha{\vskip-2pt\hskip-3pt{\scale75%\hbox{'}}\hskip1pt }<$><!--$$ όϱιστος δ $$\[--><$>\rupsilon{\vskip-2pt\hskip-3pt{\scale75%'}\hskip1pt }<$><!--$$ ας (indeterminate duality), two opposing principles, which Plato at times allowed to mix, e.g. in the Timaeus, where they constitute the world-soul in which the human soul partakes and which goes through the stages of unity, dissociation, higher unity. This triadic scheme was more explicitly developed by the neo-Platonists, especially Proclus, but also by Plotinus and Porphyry. Hölderlin must have been familiar with all this, since the relevant texts were on the compulsory reading lists during his student years (104). Given Hölderlin's influence on Hegel, this proves Henrich's thesis about the Platonist roots of German Idealism from a new angle.

How did Hölderlin conceive of the exact nature of the eccentric orbit of the human soul? To answer this, Franz reconstructs Hölderlin's mathematical background, as provided by his mathematics tutor in the Stift, Christoph Friedrich Pfleiderer (1736–1821), the greatest Euclid commentator of his time (112–4). Plato and Proclus had argued for a fundamental and irreducible geometrical distinction, namely between the ‘determinate’ and the ‘indeterminate’ line, each belonging to a distinct ontological realm, πέϱας (limitation) and $$\[--><$>\ralpha{\vskip-2.5pt\hskip-4pt{\scale75%\hbox{'}}\vskip-2.5pt{\scale95%©}}}\hskip2.5pt<$><!--$$ πειϱον (un-limitation) (109). Hölderlin mentions this distinction in a crucial, but hitherto ignored, passage in the 1795 preface to Hyperion: ‘But neither our knowledge nor our action arrives at any point of our existence there where all opposition ends, where Everything is One; the determinate line unites with the indeterminate one only in infinite approximation’. In a related letter to Schiller (4.9.1795) Hölderlin uses a geometrical example, arguing that from a theoretical and practical point of view the unification of subject and object can only be reached ‘by infinite approximation, like the approximation of the square to the circle’, and that to establish this unification in a philosophical system one would need immortality (107).

These examples show that for Hölderlin the failure of theory and practice to achieve perfection is not a contingent limitation, but is due to metaphysical principles that determine different ontological realms and are just as incompatible as the determinate and the indeterminate line in geometry (111). This was unsatisfactory for Hölderlin; perfection should be really achievable, not just in infinite approximation. He inferred that the realm of beauty was the true place of philosophy, a place that was to be reached, in finite time, through an ‘intellectual intuition’ in which all ontological difference is overcome. The path the human soul traverses here is the ‘eccentric path’, which must combine elements of both ontological realms, unity and indeterminate duality. In geometrical terms these realms correspond to the circular line and straight line respectively. Hence, the geometrical shape of the eccentric path must be a mixture of both, which means it is neither a line nor a circle. Proclus offers two more options: conic sections and spirals. Conic sections come in three varieties: ellipses, parabolas, hyperbolas. Franz rejects these, because none of them have a starting and an end point, as specified by Hölderlin. Therefore, the eccentric path must have the shape of a (finite) spiral, about which Proclus says that it is, owing its linear-circular character, a symbol of the time of the world-soul (115). The spiral is constructed out of the motion of a point along the radius of a circle, from the center to the circumference (‘ex-centric’), and the circular motion of the radius around the center of the circle. Thus, the linear and circular aspect of a spiral correspond to the two opposing principles of human existence; the circle expresses the human tendency for closure or determination, while the line the tendency to expand to infinity (118). Hence, the spiral is the symbol of human development. It is not quite clear, however, how these two human tendencies relate to the human tendencies of union and separation mentioned above. Does union correspond to determination, and separation to infinite expansion, or vice versa? Also, how does the spiral express the tendency to expand infinitely, since both motions constructing the spiral are finite? In any case, the influence of Platonist and neo-Platonist metaphysics and mathematics on Hölderlin's ideas, and through him on Hegel, is utterly remarkable.

The third section of Franz's book is dedicated to Schelling and Hegel. The first two essays deal with the philosophical significance of the fall in Schelling's Philosophie und Religion (1804) and with Christian and Platonist elements in his doctrine of Trinity in Philosophie der Offenbarung (1858). They demonstrate that we cannot understand German Idealism without taking its religious agenda seriously. The third essay, “Die Geschichte des Absoluten”, is devoted to the young Hegel's relation to the Platonist tradition, a topic researched in great detail by Jens Halfwassen, to whom Franz refers. Among other things, this essay spells out the steps which led from Hölderlin's triadic eschatology of beauty to Hegel's philosophy of identity in Jena. When Hegel moved from Bern to Frankfurt, he fell under the spell of his philosophically more advanced friend and the more libertine life in Frankfurt:

Hegel eventually conceptualises love, in the Frankfurt manuscripts ‘Liebe und Religion’, ‘Die Liebe’, ‘Glaube und Sein’, in terms very similar to Hölderlin's ‘union of union and its opposition’, writing: ‘In love the separated still persists, but not as separated, rather as united, and life feels life’ (‘Die Liebe’). Now he speaks about a union which is perfected life (‘vollendetes Leben’), because it also accounts for reflection; ‘in this [union], union and separation are united, a life which had opposed itself to itself (and now feels itself), but did not make this opposition absolute’ (221; according to Franz this is from a passage which has been left out of the new academy edition!). There is only a small step from here to the notion of ‘union of union and non-union’ presented in the Systemfragment of 1800 or the notion of ‘identity of identity and non-identity’ articulated in Differenz des Fichteschen und Schellingschen Systems der Philosophie (1801).

There are many more treasures and sources of inspiration to be found in this book. While the book lacks a bibliography, it contains beautiful illustrations relating to the various topics, such as an etching found in Voyage du jeune Anacharsis en Grèce (edited by Jean-Jacques Barthélemy, 1787). It shows young men being lectured by Plato—this book's secret hero.