Our aim is to clarify the significance and importance of Richards' theory of metaphor in his The Philosophy of Rhetoric (1936) for the history of metaphor-study. We can estimate him as a pioneer of the idea of "conceptual metaphor" in the sense of Cognitive Linguistics. I. A. Richards advocated a new philosophy of metaphor which consists of the principle of 'context' and the terminology of 'tenor' and 'media'. According to him the problems of metaphor concern not only the linguistic expressions but also our way of thinking. His terminology of 'tenor' and 'media' made a great leap in the history of metaphor-investigation because he pointed out the duality of metaphor phenomena by means of his terms. He thought that such a duality can be found not only in the linguistic expressions but also un the thoughts of our consciousness. He asserted that the metaphorical duality is a general principle which we can find in all the linguistic expressions and further in our abstract thinking even in the nonlinguistic level. Therefore we can conclude that the reason why there are metaphorical expressions is that our cognitive processes as perceiving, thinking and sensing are of metaphorical character, namely more or less 'analogical' and 'abstractive'.