We are used to thinking of words as signs of inner thoughts. In Outward Signs, Philip Cary argues that Augustine invented this expressionist semiotics, where words are outward signs expressing an inward will to communicate, in an epochal departure from ancient philosopical semiotics, where signs are means of inference, as smoke is a sign of fire. Augustine uses his new theory of signs to give an account of Biblical authority, explaining why an authoritative external teaching is needed in addition to the inward teaching of Christ as divine Wisdom, which is conceived in terms drawn from Platonist epistemology. In fact for Augustine we literally learn nothing from words or any other outward sign, because the truest form of knowledge is a kind of Platonist vision, seeing what is inwardly present to the mind. Nevertheless, because our mind's eye is diseased by sin we need the help of external signs as admonitions or reminders pointing us in the right direction, so that we may look and see for ourselves. Even our knowledge of other persons is ultimately a matter not of trusting their words but of seeing their minds with our minds. Thus Cary argues here that, for Augustine, outward signs are useful but ultimately powerless because no bodily thing has power to convey something inward to the soul. This means that there can be no such thing as an efficacious external means of grace. The sacraments, which Augustine was the first to describe as outward signs of inner grace, signify what is necessary for salvation but do not confer it. Baptism, for example, is necessary for salvation, but its power is found not in water or word but in the inner unity, charity and peace of the church. Even the flesh of Christ is necessary but not efficacious, an external sign to use without clinging to it.