It is a cornerstone of Stoic epistemology that, under certain conditions, our faculties allow us to form an infallible grasp of a state of affairs, giving rise to a state that Stoics called apprehension (katalêpsis). Until now, scholarship has mostly focused on Stoic accounts of direct, unmediated apprehension, typically achieved as a result of sense-perception. Stoics, however, complemented their account of such cases with a theory of inferential knowledge via successful inference from a sign (sêmeion) or, more specifically, by way of formulating a proof (apodeixis). Given that the extant sources on this subject are few and far between, it is unsurprising that the Stoic view on inferential apprehension is not very well understood.
R.'s monograph is a compact and ambitious study devoted to the reconstruction of this theory. In effect, it offers a detailed reading of a polemical source, the Pyrrhonist Sextus Empiricus, whose Outlines of Pyrrhonism (PH) and Against the Logicians (M 7–8) are the lengthiest and thus most important surviving sources on theories of the sign (esp. PH 2.104–6, M 8.245–56) and of proof (esp. PH 2.134–43, M 8.300–14, 411–23).
The importance of this material is matched only by its perplexity. Sextus certainly draws on Stoic material, as confirmed by his signposting as well as by parallels with other notable sources, especially Diogenes Laertius and Cicero. However, the faithfulness of his report is as much in doubt as the sources on which he relies and the identity of the thinkers whose position he purports to describe. Partly by acute analysis and partly by purposely ignoring such worries (a move he motivates on pp. 17–18), R. succeeds in outlining an appealingly clean-cut Stoic, or rather Chrysippean, theory of inferential knowledge.
The book devotes two chapters each to the logical structure and to the epistemic function of sign and proof, followed by a brief appendix on divinatory signs as well as a bibliography and indexes. Altogether, it offers a rich and illuminating study, which repays the effort it takes to work one's way through unnecessarily dense prose. In what follows I shall briefly summarise R.'s main lines of argument and highlight a few qualms about specific details.
Chapters 1–2 discuss sound conditionals and valid arguments, respectively. On R.'s view, only conditionals satisfying Chrysippus’ connexion (sunartêsis) account are acceptable to the Stoics. Connexion, on R.'s analysis, requires that the falsity of the consequent be impossible relative to (the truth of) the antecedent, and to be so in virtue of an underlying causal connection. Furthermore, an argument is valid (sunaktikos) by Stoic standards if the conjunction of the premisses and the conclusion satisfies the connexion account. In this way, not only indemonstrables and arguments reducible to indemonstrables through schemata are valid, but also non-formally valid arguments, which can be transformed into a formally valid argument (pp. 60–2).
An immediate objection to R.'s claim about the predominance of connexion is that Sextus countenances material implication as acceptable to his Stoic opponents. In response, R. shows that it is possible to read the relevant passages as specifying only the necessary condition for any true conditional (pp. 24–5). However, when it comes to the claim that it is not only possible but in fact preferable to read them in this way, his arguments are less convincing. While ‘Sextus may well – and he had better – merely give a necessary condition that is common to all accounts of the conditional and uncontested’ (p. 25), it does not follow from this that no Stoic endorsed material implication. Similarly, when claiming that Stoics would use the Stoic account of conditionals and that the Stoic account is that of Chrysippus, R. appears to beg the question. Unfortunately, he takes the suggestion that Stoic views on this matter might have evolved to be less than philosophically relevant.
Chapter 3 discusses evidence or evidentness (enargeia) while Chapter 4 – the longest and most rewarding chapter in the book – discusses revelation (ekkaluptein): the requirement that under specific conditions an evident antecedent or set of premisses must make it possible to apprehend a non-evident consequent or conclusion.
As to the former topic, R. motivates a distinction between two senses of enargeia. First, a state of affairs is evident insofar as the relevant assertible (axiôma, rendered by R. as ‘proposition’) is non-inferentially apprehensible. Second, in a ‘wider’, ‘more basic’ sense, a state of affairs is evident if the relevant assertible is either inferentially or non-inferentially apprehensible. R. unnecessarily supports his move by appealing to a contentious reading of Cicero's Lucullus 17 (from p. 76 onwards), but the distinction helps dissolve Sextus’ chief argument for the impossibility of revelation (see, e.g., PH 2.116, 167–8, M 8.266–8) by showing that it trades on the ambiguity of the two senses of evidentness. It also rebuts the modern charge that Stoics cannot allow for chains of proofs by showing that the conclusion of one proof can serve as an evident premiss in another proof (see esp. pp. 88–90).
As for the notion of revelation, R.'s treatment turns on a novel and largely convincing interpretation of the distinction between arguments that are merely progressive and arguments that are both progressive and revelatory (PH 2.141–3, M 8.307–9). He shows that the distinction is not a matter of the type of conditionals involved – and, in doing so, he vindicates Sextus’ controversial definition of Stoic signs (PH 2.104) – but rather of the relation between premisses and conclusion. Merely progressive arguments depend on trust and memory while the premisses of a revelatory argument possess the power (dynamis) of transmitting their evidentness to the conclusion they support. Put differently, only revelatory arguments identify the right sort of connection between the bodies that serve as truthmakers of the assertibles involved in the premisses and the conclusion (p. 130). Consequently, while a merely progressive argument may satisfy the requirement of infallibility, only a revelatory argument can produce apprehension.
This illuminating analysis is accompanied by a few loose threads. Apart from explaining away the role of memory in progressive arguments as a mere jab at Platonic anamnesis (pp. 140–1), R. adds a few superficial remarks on Stoic internalism about inference (p. 142 with footnote 264). This hasty afterthought excludes the unintuitive but intriguing option of a thoroughgoing Stoic externalism.
Most importantly, R. argues for a Stoic ban on using less than revelatory arguments. As he puts it, non-sages de facto assent to the conclusions of merely progressive arguments, but the Stoic sage would only ever rely on a revelatory one (pp. 104, 137). This supposed ban needs qualification, first, in light of the fact that Sextus illustrates merely progressive arguments by invoking the trust placed in Zeus himself and, second, because it fails to take note of appeals to trust in early Stoic descriptions of the sage. Would the Stoic sage really not assent to a genuine pronouncement of the head of the Greek pantheon or the advice of a fellow wise person? Last but not least, R. criticises the Stoic view for its single-minded application of an unrealistically demanding epistemic standard across the board (p. 146). A more charitable reading could start from the concession that the Stoics did not apply the same standard in all relevant contexts.
These are minor concerns. R.'s study is a successful, novel account of an important and not yet quite understood piece of Stoic theorising. It will undoubtedly be a standard reference point for specialists of Stoicism, ancient logic and Sextan Pyrrhonism.
