The Greek notion of beauty (to kalon) encompasses not only nature and artifice, but also the Good. This paper explains the connection by interpreting Plato in a way that allows his theory to be developed beyond the confines of his philosophy. It is argued that we could read his theory of beauty as based on fineness of appearance. This arises when a sensory particular transcends itself and suggests the presence of its sustaining Form, or when sophrosynē in human agency discloses the Good’s power to transform the sensible world. In both cases, there is a pleasure in how certain phenomena or agents manifest the influence of the Forms at the sensory level. Beauty centres on an Ideal relation. By critically revising Plato’s position and taking it beyond the context of exegetical debate, a generally viable explanation of the grounds of Ideal beauty is formulated. This clarifies how such beauty is based on both the fundamental conditions of knowledge, as such, and our existence as free beings. Ideal beauty is shown, also, to be an aesthetic concept with enduring importance.