 Unlike modern anti-skeptical lines of argumentation, Augustine’s refutation of skepticism does not aim at justifying our ordinary practices and beliefs. To refute the Academic claim that, since the wise person can never be sure whether she has grasped the truth, she will consistently withhold assent in order not to succumb to empty opinion, he thinks it sufficient to demonstrate the existence of some kind of knowledge that is immune to skeptical doubt. His strategy therefore consists in pointing out 1) the certainty of self-referential knowledge (the wise person “knows wisdom”, Contra Academicos 3.6; the Academic skeptic “knows” the Stoic criterion of truth, ib. 3.18–21); 2) the certainty of private or subjective knowledge (I am certain that something appears white to me even if I am ignorant whether it is really white, ib. 3.26); 3) the certainty of formal, logical or mathematical, structures (ib. 3.24–29), knowledge of which is possible independently of the mental state of the knower, whereas the reliability of sense impressions differs according as we are awake or dreaming, sane or insane. Modern critics have not been very impressed by these arguments (e.g., Kirwan 1989: 15–34), and an ancient skeptic would rightly have objected that being limited to subjective or formal knowledge, they could not justify the dogmatists’ claim to objective knowledge of reality (cf. Sextus Empiricus, Outlines of Pyrrhonism 1.13). Yet this is not Augustine’s point. To him it matters to have shown that even if maximal concessions are made to skepticism concerning the unknowability of the external world attainable by the senses, there remains an internal area of cognition that allows for and even guarantees certainty. This is why Contra Academicos ends with a sketch of Platonic epistemology and ontology and with an idiosyncratic if not wholly unparalleled reconstruction of the history of the Academy according to which the Academics were in fact crypto-Platonists who hid their insight into transcendent reality and restricted themselves to skeptical arguments to combat the materialist and sensualist schools dominant in Hellenistic times until authentic Platonism emerged again with Plotinus (Contra Academicos 3.37–43; the story is still told in Letter 118 of 410, where the renaissance of Platonism is however connected with the rise of Christianity). The only realities that meet the Hellenistic criterion of truth and guarantee absolute certainty by being self-evident are the Platonic Forms (Contra Academicos 3.39; cf. De diversis quaestionibus 9; Cary 2008a: 55–60). The “objects” of knowledge that appear in Augustine’s anti-skeptical arguments thus either are the Platonic Forms themselves or at least point out the way of accessing them. This squares with the early Augustine’s tendency to interpret the Forms, or at any rate the most basic among them, as “numbers”, i.e., as the formal and normative structures and standards that govern all reality and enable us to understand and evaluate it (De ordine 2.14; 16; De musica 6.57–58; O’Daly 1987: 101–102; see also  5.2 Illumination).  Strictly speaking, Augustine’s anti-skeptical arguments do not justify the claim that knowledge can be derived from the senses; having sensible and mutable objects, they cannot but yield opinion or, at best, true belief. The later Augustine, in a more generous way of speaking, widens the term “knowledge” (scientia, to be distinguished from “wisdom”, sapientia) so as to include what we learn through sense perception and from reliable witnesses (De trinitate 15.21; cf. De civitate dei 8.7; Retractationes 1.14.3; Siebert 2018; see  5.3 Faith and Reason).