The notion of conjugation("Katsuyoo") in traditional Japanese grammar which was found on the basis of contrast with Sanskrit noun declension in the Kamakura period or even earlier, and was compiled and strictly formulated in the days of Tokugawa shogunate, has been taught even now(or has been considered to be taught) as a central concept of school grammar in both junior high schools and high schools. The "Katsuyoo" chart consists of six forms. Three of them, such as Shuushikei, Kateikei and Meireikei play syntactical roles in a sentence just as they are, and are recognized as a part of conjugation in a real linguistic sense. However, both forms Mizenkei and Kateikei are only used in conjunction with either postpositional particle or auxiliary verbs, thus must be considered as stem transformation. On the other hand, Ren`youkei possesses both functions. Conclusively speaking, the "Katsuyoo" system is a mix of a part of conjugation and stem transformations. However, teachers of school grammar haven`t quite reached this realization and as a result, students have been experiencing a difficulty in obtaining unified understanding of "Katsuyoo" system. I am afraid this hard-to-grasp notion in school grammar has been a cause of indifference and ignorance of the Japanese toward the grammar of their own language. A new grammar has already been created, as proposed by KIYOSE Gisaburo in the 1970`s. This makes Japanese grammar simpler and gives us orderly description by using a "union" vowel and consonant. But it has not yet reached the stage of being introduced in school education. I would suspect that the reason comes from following background: The "Katsuyoo"-dependent traditional school grammar of present-day Japanese is situated in school educational system as pre-training before leaning the "Katsuyoo"-dependent traditional classical grammar to read and interpret classic Japanese. Those who criticize "Katsuyoo"-dependent grammar are forced into double responsibilities - completing grammar of present-day Japanese, and elaborating simple and plain grammar which enables leaner to read classic Japanese, using the same grammatical concept and terminology of former grammar.