The three dogmas. The "middle" school of Tiantai says 即空, 即假. 即中 i.e. 就是空, 假, 中; (a) by 空śūnyais meant that things causally produced are in their essential nature unreal (or immaterial) 實空無; (b) 假, though things are unreal in their essential nature their derived forms are real; (c) 中; but both are one, being of the one 如 reality. These three dogmas are founded on a verse of Nāgārjuna's-- 因緣所生法, 我說即是空, 亦為是假名, 亦是中道義 "All causally produced phenomena, I say, are unreal, Are but a passing name, and indicate the 'mean'." There are other explanations-- the 圓教 interprets the 空 and 假 as 中; the 別教 makes 中 independent. 空 is the all, i.e. the totality of all things, and is spoken of as the 真 or 實 true, or real; 假 is the differentiation of all things and is spoken of as 俗 common, i.e. things as commonly named; 中 is the connecting idea which makes a unity of both, e.g. "all are but parts of one stupendous whole." The 中 makes all and the all into one whole, unifying the whole and its parts. 空 may be taken as the immaterial, the undifferentiated all, the sum of existences, by some as the tathāgatagarbha 如來藏; 假 as the unreal, or impermanent, the material or transient form, the temporal that can be named, the relative or discrete; 中 as the unifier, which places each in the other and all in all. The "shallower" 山外 school associated 空 and 中 with the noumenal universe as opposed to the phenomenal and illusory existence represented by 假. The "profounder" 山內 school teaches that all three are aspects of the same.