Language with a purely logical dimension is desirable in legal document s and in scientific and philosophical treatises, where clarit y, precision, and singleness of meaning are requisite. Consequently, synonyms, which usually vary in shades of meaning, ought to be avoided, and the same word should be employed throughout to convey the same meaning; or if it is used with a different meaning, that fact should be made clear. Abstract words are usually clearer and more precise than concrete words, for abstract knowledge is clearer, although less vivid, than sense knowledge. Yet to communicate abstract knowledge, one should employ concrete illustrations from which the reader or listener can make the abstraction for himself since by so doing he grasps the abstract ideas much better than if the writer or speaker gave them to him ready-made.