柏拉圖在《大希皮亞斯》304e 和《理想國》497d中分別聲稱「美的事物是困難的」。從他的斷言中，我們可以知道，美這個主題是如此之難，連柏拉圖這樣的偉大哲學家也不得不做出這樣的感嘆。這篇論文就是以《大希皮亞斯》為基礎來思考柏拉圖的美。「什麼是美？」和「什麼是美的？」是柏拉圖《大希皮亞斯》中蘇格拉底與希皮亞斯爭論的核心。蘇格拉底涉及理知之美，希皮亞斯涉及感性之美。在它們之間有中間官能，柏拉圖稱之為「靚」（τὸ κάλλος），他並進一步將其分為「創作品之靚或物體之靚」和「學習之靚」以駁斥智辯者對美的主張，並證明後者對美的概念是無知的之外，更進一步表明知識（或真理）、德性和美的事物是三者一體的。顯然，這篇文章是從蘇格拉底的「美」與希皮亞斯的「美的」的差異及其與德性的連結開始，逐步深入討論美、靚和美的。

Plato in the Greater Hippias 304e and the Republic 497d claims that ‘the beautiful things are difficult’ (‘χαλεπὰ τὰ καλά’). From his assertion, we can know that the subject of beauty is so difficult that even great philosophers such as the man himself had to lament. This paper is based on the Greater Hippias to inquire into Plato’s concept of beauty. ‘What is beauty?’ and ‘what is beautiful?’ are at the core of Socrates’s and Hippias’s debates in Plato’s Greater Hippias. Socrates is concerned with the beauty of noesis, while Hippias is involved in the beauty of aesthesis. Between them there is the middle faculty (τὸ μεταξύ), which Plato calls τὸ κάλλος (fairness), and which he further divides into ‘τὸ κάλλος τοῦ σώματος’ and ‘τὸ τῶν μαθημάτων κάλλος’ to refute the Sophists’s assertation of beauty and to show that the latter are ignorant of the concept of beauty, by means of which he further shows that knowledge (or truth), virtue and beauty are tripartite. This paper essays to discuss in depth beauty (τὸ καλόν), fairness (τὸ κάλλος) and beautiful (καλόν) from the difference between Socrates’s ‘τὸ καλόν’ and Hippias’s ‘καλόν’ and their connection with virtue.