Grammatical ites of elementary Japanese appear to be easier than those of intermediate or advanced Japanese but errors or nonuses are more frequently seen on elementary items rather than intermediate or advanced ones, showing that learners don’t have sufficient grammatical knowledge to use them in actual situation though they themselves believe that they have. On the other hand, grammar tends to give negative impressions to leaners that discourage their motivation to study it, such as that there are too many things to memorize or that it goes too further into details to tell what are import or why they are necessary or that it permits too many exceptions.Raising such problems, we will discuss vital points of grammatical description that lead to appropriate uses through the observation of familiar errors on the elementary grammatical items, such as wa vs. ga, transitive verbs vs. intransitive verbs,-te iru, passives,-te kureru, daroo-ka,-tara vs.-temo etc. “Vital points” include “pitfalls”(the learners’ misunderstandings in which they are apt to fall) and “neccesities”(the irreplaceable raison d’être of the item) as their important factors. The accurate grasp of “vital points” would not only contributes to support the leaners’ acquisition of grammar but also leads to the deveropment of descriptive study of grammar.