 Augustine deploys what we may call his philosophy of the mind most fully in his great work on Nicene Trinitarian theology, De trinitate. Having removed apparent Scriptural obstacles to the equality and consubstantiality of the three divine persons (bks. 1–4) and having set out the grammar, as it were, of adequate speaking about the Trinity by distinguishing absolute and relative propositions about God and the three Persons (bks. 5–7; King 2012), he turns to an analysis of the human mind as an image of God (bks. 8–15; Brachtendorf 2000; Ayres 2010; Bermon &amp; O’Daly (eds.) 2012). The basis for this move is, of course, Genesis 1:26–27. Augustine follows a long-standing Jewish and Patristic tradition, familiar to him from Ambrose, according to which the biblical qualification of the human being as an image of God referred not to the living body (a literalist reading vulnerable to the Manichean charge of anthropomorphism, cf. Confessiones 6.4) but to what is specifically human, i.e., the “inner man” (2 Corinthians 4:16, quoted, e.g., in De trinitate 11.1) or the mind (mens). Assuming, in a Platonist manner, that “image” in this case does not merely mean an analogy but a causal effect of the original that reflects the essential features of the latter on a lower ontological level, he scrutinizes the human mind for triadic structures that meet the Nicene requirements of equality and consubstantiality and may thus give a—however faint—understanding of the Triune God. The general pattern of his argument is the Augustinian ascent from the external to the internal and from the senses to God; but since human reason is, whether by nature or due to its fallen state, hardly capable of knowing God, Augustine this time is obliged to interrupt and re-start the ascent several times. The final book shows that the exercise of analyzing the human mind does have preparatory value for our thinking about the Trinity but does not yield insight into the divine by being simply transferred to it (De trinitate 15.10–11). The three elements Augustine discerns in all our cognitive acts from sense perception to theoretical reason or contemplation are: [1] an object that is either external to the mind (as in sense perception) or internal to it, in which case it is an image or a concept stored in our memory; [2] a cognitive faculty that must be activated or “formed” by the object if cognition is to come about; [3] a voluntary or intentional element that makes the cognitive faculty turn to its object so as to be actually formed by it. The last element ensures the active character of perception and intellection  but also gives weight to the idea that we do not cognize an object unless we consciously direct our attention to it (MacDonald 2012b). Though this triadic pattern is operative on all levels of human cognition, Augustine contends that only the mind’s intellectual self-knowledge on the level of contemplative reason (its “memory of itself, knowledge of itself and love of itself”) qualifies as an image of God because only here are the three elements as closely related to each other as in the Nicene dogma and because they are as inalienable as the mind’s immediate presence to itself (De trinitate 14.19). This idea is carefully prepared in Book 10, which contains one of Augustine’s most remarkable arguments for the substantiality of the mind and its independence of the body (Stróżyński 2013; Brittain 2012a; Matthews 2005: 43–52; Bermon 2001, 357–404). Augustine begins by arguing (in a manner reminiscent of his cogito-like argument; see  5.1 Skepticism and Certainty)  that the mind always already knows itself because it is always present to and hence aware of itself. This pre-reflexive self-awareness is presupposed by every act of conscious cognition. If so, however, the Delphic command “Know thyself” cannot mean that the mind is to become acquainted with itself as if it had been unknown to itself before, but rather that it must become conscious of what it knew about itself all along and distinguish it from what it does not know about itself. As the mind in its fallen state is deeply immersed in sensible reality, it tends to forget what it really is and what it knows it is and confounds itself with the things it attaches the greatest importance to, i.e., sensible objects that give it pleasure. The result are materialist theories about the soul, which thus derive from flawed morality (De trinitate 10.11–12). If it follows the Delphic command, however, the mind will realize that it knows with certainty that it exists, thinks, wills etc., whereas it can at best merely believe that it is air, fire or brain (ib. 10.13).  And as the substance or essence of the mind cannot be anything other than what it knows with certainty about itself, it follows that nothing material is essential to the mind and that its essence must be sought in its mental acts (ib. 10.16). Full self-knowledge is reached, then, when the mind’s inalienable self-awareness (se nosse, “to be acquainted with oneself”) is actualized to conscious “self-thinking” (se cogitare). How this relates to the mind’s pre-reflexive presence to itself is not entirely clear (for problems of interpretation, see, e.g., Horn 2012; Brittain 2012b), but Augustine seems to think that not only the mind’s intellectual self-thinking but already its immediate self-awareness is triadically structured and an image of the Triune God (De trinitate 14.7–14). Again, the ethical side of the theory should not be overlooked. As a strong voluntary element is present in and necessary for an act of cognition, what objects (imaginations, thoughts) we cognize is morally relevant and indicative of our loves and desires. And while the triadic structure of the mind is its very essence and hence inalienable, Augustine insists that the mind is created in the image of God, not because it is capable of self-knowledge, but because it has the potential to become wise, i.e., to remember, know and love God, its creator (ib. 14.21–22).