In his writings Philosophical Remarks, the Austrian-British Philosopher Ludwig Wittgenstein draws an octahedron with the words of pure colours such as “white”, “red” and “blue” at the corners and argues: “The colour octahedron is grammar, since it says that you can speak of a reddish blue but not of a reddish green, etc”. He uses the word “grammar” in such a specific way that the grammar or grammatical rules describe the meanings of words/expressions, in other words, how we use them (...) in our language. Accordingly, the colour octahedron can also be taken to represent grammatical rules about how we apply words of colour, e.g., that we can call a certain colour “reddish-blue”, but not “reddish-green”. In a different context, the Japanese philosopher Shūzō Kuki explores in his work The Structure of Iki what the Japanese word “iki” means. This word is often translated as “chic” or “stylistic” in English, but Kuki holds that it is an aesthetic Japanese concept that cannot be translated one-to-one, instead encompassing three aspects: “coquetry”, “pride and honour” and “resignation”. To explain the meanings of the word “iki” and other related words all of which Kuki calls “tastes”, he introduces a rectangular prism as a geometrical representation similar to Wittgenstein’s colour octahedron. In this paper, I argue that the rectangular prism does not solely explain how the modes of Japanese tastes are related to each other, but also has a grammatical character. On this score, I suggest that one can regard this rectangular prism as a description of the grammatical rules of the Japanese language. By appeal to the arguments of both philosophers and in comparison with them, I will not only clarify what they claim by geometrical representations but also examine what role this kind of representation plays as an explanation of grammar in general. Keywords: grammar, colour octahedron, rectangular prism, Shūzō Kuki, Wittgenstein. (shrink)