 Augustine’s theory of knowledge—his so-called doctrine of illumination—is a distinctly non-empiricist epistemology based on a probably Neoplatonic reading of Plato’s doctrine of recollection (Burnyeat 1987; MacDonald 2012b; King 2014a: 147–152; Karfíková 2017). Like Plato and his followers, Augustine thinks that true knowledge requires first-hand acquaintance; second-hand information, e.g., from reliable testimony, may yield true and even justifiable belief, but not knowledge in the strict sense.  In the case of sensible objects—which, strictly speaking, do not admit of knowledge at all but only opinion—such  first-hand acquaintance is possible through sense perception. Cognition of intelligible objects, however, can be neither reached empirically by means of abstraction nor transmitted to us linguistically by a human teacher (see  5.4 Language and Signs);  rather, such cognition requires personal intellectual activity that results in an intellectual insight, which we judge by a criterion we find nowhere but in ourselves. The paradigm of this kind of cognition are mathematical and logical truths and fundamental moral intuitions, which we understand not because we believe a teacher or a book but because we see them for ourselves (De magistro 40, cf. De libero arbitrio 2.34). The condition of possibility and the criterion of truth of this intellectual insight is none other than God (a view attributed, with explicit approval, to the Platonists in De civitate dei 8.7), who, in the manner of a Neoplatonic immaterial principle, is both immanent and transcendent in relation to our soul. Augustine mostly explains this Platonizing theory of a priori knowledge by means of two striking images: the inner teacher and illumination. The former is introduced in the dialogue De magistro (ca. 390) and remains frequent especially in the sermons (e.g., In epistulam Iohannis ad Parthos tractatus decem 3.13; Fuhrer 2018b); according to it, Christ is present in our souls and by “presiding over” them like a teacher guarantees the truthfulness of our understanding (De magistro 38–39, cf. Ephesians 3:17 for the image and, for the idea that truth “lives in the inner man”, De vera religione 72). The latter appears first in the Soliloquia (1.12–15) and is ubiquitous in Augustine’s writings (cf. esp. De trinitate 12.24). It is ultimately derived from the Analogy of the Sun in Plato’s Republic (508a-509b; cf. Rist 1994: 78–79). In the Soliloquia Augustine says, in a manner strongly reminiscent of Plato, that just as the sun is both visible itself and illumines the objects of sight so as to enable the eye to see them, God is intelligible himself and illumines the intelligible objects (which are here identified with the objects of the liberal disciplines and subordinated to God) so as to enable reason (the “eye” of the soul) to activate its capacity for intellection. The later version in De trinitate explicitly presents divine illumination as an alternative to Platonic recollection and situates it in the framework of a theory of creation. Here Augustine says that the human mind has been created by God in such a way as to be “connected” to intelligible reality “from below” (subiuncta) and with a capacity (capacitas) that enables it to “see” the intelligibles in the light of intelligible truth, just as the eye is by nature able to see colors in the light of the sun. Obviously, “capacity” in this case does not mean pure potentiality (as in the tabula rasa theory endorsed by Augustine’s interlocutor Euodius in De quantitate animae 34) but comprises at least implicit or latent knowledge of moral and epistemological standards. Both images, if properly read, should preclude the misunderstanding that Augustine’s gnoseology makes human knowledge entirely dependent on divine agency, with the human being becoming merely a passive recipient of revelation (cf. Gilson 1943: ch. 4 and Lagouanère 2012: 158–180 for the debates about Augustinian illumination in medieval and modern philosophy). Cognition does not simply result from the presence of Christ in our soul but from our “consulting” the inner teacher, i.e., our testing propositions that claim to convey a truth about intelligible reality (or even a general truth about sensible objects, cf. Letter 13.3–4) against the inner standards we possess thanks to the presence of Christ (De magistro 37–38; this way of “consulting” the inner truth is repeatedly dramatized in the Confessiones, e.g., 11.10; 11.31; Cary 2008b: 100). And while every human being is “illumined” by the divine light at least from behind so as to be able to pass true judgments about right and wrong or good and evil, in order to develop these natural intuitions to full knowledge or wisdom and to be able actually to lead a virtuous life, we need to convert to God, the “source” of the light (De trinitate 14.21). Thus, while all human beings are by nature capable of accessing intelligible truth, only those succeed in doing so who have a sufficiently good will (De magistro 38)—presumably those who endorse Christian religion and live accordingly. This strong voluntary element intimately connects Augustine’s epistemology with his ethics and, ultimately, with his doctrine of grace (on the parallel structure of cognition and grace in Augustine see Lorenz 1964). Like all human agency, striving for wisdom takes place under the conditions of a fallen world and meets the difficulties and hindrances humanity is subject to because of original sin.