Abstract: What is the true meaning of commonly used alkaline and sub-alkaline curves? It is reasonable for the International Union of Geological Sciences to make the requirement that alkaline rocks must have actual alkaline minerals and/or feldspar appearance as markers. However, the International Union of Geological Sciences also agrees that the basalt in area B of the TAS diagram could be subdivided into alkaline basalt and sub-alkaline basalt, depending on whether they have standard mineral nepheline. The basalt of the standard mineral nepheline is classified as alkaline basalt, while the Hawaiian rock is the alkaline basalt, due to the existence of standard minerals of nepheline. Why do they appear in the two districts on the TAS diagram (alkaline basalt in area B, Hawaiian Rock in the S1 area), and is this a conceptual confusion? It seems that the previous academic definition of alkaline and alkaline rock is somewhat confusing, the alkaline-sub-alkaline boundary determined by many experts is not the tholeiite and alkaline series, but is between normal series and dolerite series. In this paper, the global volcanic rock data are used to investigate TAS diagram and alkaline-sub-alkaline boundary, and it is found that alkaline and alkaline rocks are defective in the interpretation of terms and thus this paper proposes solutions. This matter involves the basic theory of petrology, to which the academia should pay more attention.