Lloyd Gerson’s latest book issues a challenge to contemporary philosophers to rethink the nature of their vocation, its problems, presuppositions, and ends. Gerson bucks the mainstream to affirm that naturalism in all its varieties, reductive as well as liberal, is a dead-end and that if philosophy is possible at all as a branch of knowledge distinct from the natural sciences, with a subject-matter of its own, then it is possible only as Platonism. The forcefulness and clarity with which he makes his case demand and deserve the attention of a wide philosophical audience.
Throughout, Gerson’s argumentation is historically and hermeneutically sensitive. He draws his arguments mainly from Plato’s dialogues (chiefly Phaedo, Republic, Theaetetus, Sophist, Parmenides, Philebus, and Timaeus); he makes measured use of the sources (primarily Aristotle) for Plato’s unwritten doctrines, on which he also draws, and he is sensitive to the breadth of opinion on matters underdetermined by the core doctrines of Platonism. Nor is the target of Gerson’s criticism a straw man. He identifies the positions of the Platonists’ naturalist opponents (e.g. Anaxagoras, the Stoics, the Epicureans), those of contemporary naturalists, and their systematically relevant common ground (e.g. chs. 1, 2.2–2.3). In keeping with his conception of Platonism’s defining commitments, Gerson’s arguments target fundamental doctrines and their consequences. With the possible exception of Chapter 4, whose arguments are unusually compressed, the style is perspicuous, even as the book’s wealth of argumentation defies summary in a short review.
The author’s distinctive views on Plato and Platonism play an indispensable role in his argument, though the self-contained presentation does not presume familiarity with his other publications. The book impresses most by the way it combines its depth of hermeneutic and analytical detail with a far-reaching perspective on what is at stake philosophically and for philosophy itself. Accordingly, this review focuses on the systematic line of argument highlighted in the book’s title. The first and final chapters neatly frame this line of argument. Platonism is identical with systematic philosophy itself and Platonism is fundamentally incompatible with Naturalism, so we ought to reject as unstable positions that try to compromise by incorporating Naturalist elements into Platonism or vice versa. Metaphysical commitment to the reality of the intelligible world is uniquely capable of grounding epistemology and normative ethics; if Platonism is indefensible, then not only must we give up on any distinctively philosophical subject-matter, we must accept relativism and skepticism as the only alternatives.
Gerson develops this line of argument through his transparently structured book. Chapters 2 and 3 reflect his view that the negative and positive sides of Platonism are mutually supporting. The first of these introduces Platonism in terms of five “antis” (18): antinominalism, antimaterialism, antimechanism (i.e. rejection of causal closure of the physical), antirelativism, and antiskepticism. That materialism and causal closure are core doctrines of Naturalism is hardly controversial; Gerson argues in addition that consistent materialism entails nominalism, relativism, and skepticism (e.g. 22 ff., cp. 99 ff.). By virtue of its basic rejection of these doctrines, Platonism is constitutively Antinaturalist, and because of the tight conceptual link among the doctrines, there can be no stable rapprochement between Platonism and Naturalism (32 ff.). Chapter 3 focuses in on the theoretical interplay between the theory of Forms and Plato’s central criticism of Naturalism, namely its “inadequacy […] to give adequate explanations generally” (75). Briefly, explanation requires identification of a cause. To seek to reduce causation to a putative set of necessary (and supposedly jointly sufficient) conditions is to court tautology; the cause or explanans must be distinct in kind from the effect or explanandum, not just a statement of what the relevant state of affairs consists in or when it can be said to obtain (chs. 3.3–3.4).
Chapters 4–6 are at the heart of the book’s constructive philosophical project, constituting a sustained defense of full-fledged Platonism, that is, a metaphysical Derivationssystem (161 f.) comprising a first principle (the Good or the One) and an eternally active intellect that is cognitively identical with the array of Forms, whose multiplicity-in-unity it explains (85 f., 96), and which are in turn the truth-makers for judgments about the sensible no less than the intelligible world (143 f.). The focus of Chapter 4 is logical and epistemological. Gerson argues that “the function of Forms is to explain the possibility of true nonexclusive predication” (84), for which Naturalism is unable to provide a metaphysical foundation. For that we need immaterial Forms. A Form is neither a particular nor a hypostasized universal (so Platonism differs from both realism and conceptualism), but rather a metaphysically distinct “one-over-many” (76–82). The array of internally related Forms are “eternal natures” whose omnipresence explains both possibilities and why those possibilities are actualized under the appropriate physical conditions (98).
The associated epistemology is demanding: knowledge must be of being and it must be infallible (108 f.). Consequently, it is false to characterize knowledge as true belief together with an account, for knowledge is a non-propositional, unmediated cognition of Forms, a “direct seeing of something knowable” (114). As such, it is inerrant, lacking the minimal representational complexity required for error (116). Furthermore, because the Forms are all internally related and knowable only in light of the Good, knowledge must be “as comprehensive as the entire array of intelligible Forms” (116). Gerson’s argument for this conception of knowledge pivots on our ability to judge things as being deficient in regard to a predicate f that is nevertheless correctly predicated of them. Our ability to make such judgments indicates that “F-ness” is something above and beyond any particular instance of f, and that there must be prior, self-reflexive (hence indefeasible), knowledge of F-ness when we do make such judgments. Gerson finds here materials for an antimaterialist argument (110), concluding the chapter with the argument that “only an immaterial entity can have beliefs about the sensible world,” because “the cognition of a one-many requires self-reflexivity and […] only an immaterial entity can have that” (118).
In the course of making the exegetical argument (ch. 5) that the Idea of the Good as the first principle is ubiquitous in Plato’s dialogues, Gerson reconstructs the main lines of the Platonic Derivationssystem, explaining the sense in which the Good is “beyond essence” yet apprehensible, and in what sense the Forms are “good-like” (126 ff.). The absolutely simple superordinate Idea of the Good (the ‘One’) is to be distinguished from the unity of coordinate Forms (including the Form of the Good: cp. 158, 163 ff.), by way of which it is causally efficacious in both the intelligible and sensible world (171). We cognize the One abductively through instances of self-sufficiency (134 f.). In order to explain how being (i.e. the total array of Forms) is both complex and unified, Platonism requires both the doctrine of the superordinate One as first principle of all and the doctrine of the eternal intellect. The intellect is good-like by functioning to impart integrative unity (i.e. intelligibility, “ontological truth”: 149 ff.) to things, and things in their turn are good or good-like in virtue of possessing integrative unity (151). Importantly, Gerson does not understand the Forms to be independently efficacious; he expands on the argument from Chapter 3 that explanatory adequacy requires the causal efficacy of the Good, instrumentally mediated by the eternal intellect operating in and according to the Forms (154). The explication of this system was and is the central task of Platonism, whose systematic character is crucial to critical engagement with Naturalism (154 f.).
Chapter 6 rounds out Part One with a discussion of Platonism’s normative significance: While naturalism can account for the distinctness of the real from the merely apparent good and so secure the objectivity of ethical value relative to individuals, it must fail in combining objectivity with ethical universality and necessity. To achieve universality and ground non-natural normativity, ethics needs Platonism. Platonism affirms a fundamentally normative (teleological) dynamic for the universe in its entirety: the metaphysics of “remaining”, “proceeding”, and “reverting” to the Good (189 f.). It thereby provides a uniquely adequate framework for understanding the relation between virtue and knowledge, what goodness consists in, and which (kinds of) things are good, while also laying the foundation for the theory of freedom and personal moral responsibility (190 ff.). Readers who are otherwise in agreement with Gerson’s emphasis on the independence, unity, and explanatory relevance of the intelligible sphere might still take issue with this (albeit genuinely and characteristically Platonic) causal conception of the Good. Can the Good be both a causal force and the source of normativity and human freedom?
Part Two examines developments in Platonism after Plato. As in Part One, Gerson deftly interweaves the historical and hermeneutic with the systematic strand of his argument. To focus on the latter, he advances his argument for the fundamental incompatibility of Platonism and Naturalism in three distinct points. First, he argues in Chapter 7, on Platonic-Aristotelian grounds, that physics cannot take the place of metaphysics (prima philosophia) as an inquiry into being qua being. Far from its being the case that if (contrary to fact) there were no immaterial intelligible world, then the study of nature would be the universal science of being, it is rather true that in the absence of the intelligible world there would be no unifying principles and hence no science at all (201). The notion of a physicalist ontology is obviously a non-starter from this point of view. Second, drawing on the Platonic results of Chapters 4 and 5, Gerson reconstructs Aristotle’s arguments for the immateriality of intellect and its metaphysical distinctness from the soul or any faculty of the soul. Thus, despite Aristotle’s acknowledged disagreements on certain points of doctrine (e.g. the immortality of the soul, the First Principle’s superessentiality), he remains a thoroughgoing Antinaturalist (197 f.). Third (ch. 8), Gerson reconstructs Plotinus’ criticism of the incoherence of Stoic attempts to integrate Platonism and Naturalism, in their epistemology and ethics no less than in the materialism with which they sought to replace the metaphysics of an immaterial intelligible sphere.
The penultimate Chapter 9 is aptly titled “Proclus and Trouble in Paradise.” Here Gerson thematizes challenges to Platonism arising from within the Platonic tradition, specifically problems that come to a head in the thought of Damascius and which cast doubt on both the intelligibility and the causal / explanatory relevance of the First Principle. Though it is beyond the scope of Gerson’s book to address the “perhaps irresolvable tension between the absolute simplicity of the one and its explanatory adequacy for any ‘many’”, he frankly admits the gravity of the problem and its significance for the project as a whole: “The alternative to Naturalism of any sort, and along with that the possibility of philosophy, depends upon the resolution of this tension” (260).
The book thus ends with a cliffhanger. If philosophy is possible, it is possible only as Platonism; but the viability of Platonism is problematic for reasons internal to the Derivationssystem itself. Beyond the stark clarity of “Platonism or bust,” what does this give us to work with? Gerson himself explicitly suggests one positive implication: an approach to studying and teaching the history of philosophy as an ongoing struggle between Platonist and Naturalist tendencies and the various compromises the two have struck or perhaps rather been forced to suffer (265). A further obvious, though doubtless controversial implication holds for how to understand the (singular?) philosophical project as such; a robust renewal of this debate in light of Gerson’s points is desirable. Finally, Gerson’s book suggests that if we take philosophy seriously, we ought to take Platonism seriously as a well-defined and ongoing program of philosophical research. To acknowledge this imperative is to acknowledge the contemporary relevance of a systematic style of philosophizing (exemplified by, inter alios, Spinoza, Hegel, and Bradley: cp. 261), that 20th– and 21st-century philosophers have mostly eschewed. Gerson makes a thought-provoking case for renewed exploration of a unified, broadly idealist metaphysics of the true, the right, and the good in their systematic interrelations.