paragraph:  In the second place, you should obtain specific and detailed command of general ideas.  Not of out-of-the-way ideas.  But of the great basic ideas that are the common possession of all mankind.  For through these basic ideas is the most natural and profitable approach to the study of synonyms.  Each of them is represented by a generic word.  So elementary are idea and word alike that a person cannot have the one in mind without having the other ready and a-quiver on his tongue.  Every person is master of both.  But it is unsafe to predicate the person's acquaintance with the shades and phases of the idea, or with the corresponding discriminations in language.  He may not know them at all, he may know them partially, he may know them through and through.  Let us suppose him ignorant of them but determined to learn.  His progress, both in the thought and in the language, will be from the general to the specific.  His acquaintance with the idea in the large he will gradually extend to an acquaintance with it in detail, and his command of the broad term for it he will little by little supplement with definite terms for its phases.  An illustration will make this clear. 
question: Why should you obtain specific and detailed command of general ideas?
answer: Because it is the most natural and profitable approach to the study of synonyms