The current studies on Plato's perception-theory concentrate mainly on the analysis of the different acts performed by sense-perception. For Plato, however, such an analysis is indeed a consequence of his systematic perception doctrine: Primarily he has explored the more fundamental issues, i.e. why the world in which we live is perceptible at all, and which abilities we human beings must constitutionally have to discriminate and comprehend the perceptible objects. In this fact, interpretating Plato's explanation of these questions in a comprehensive view is the target of this research.