But the definition of a library as a book or books kept for use only brings us up against the farther question, What is a book? To this it may be answered that a book is any record of thought in words. Here again neither size, form, nor material matters; even a one word record may be a book and that book a library. This leads again however to still another question: What is a word? Without stopping to elaborate or to discuss definitions in detail, we may take the next step and define a word as “any sign for any thing”, and again explain the sign as anything which points to something other than itself. This is not an arbitrary definition but one founded in modern psychology and philology and to be found in sundry stout volumes by Marty, Leroy, Wundt, Dittrich, van Ginneken, Gabelentz, and others. The sign may be a sound, a color, a gesture, a mark or an object. In some stenographic systems a single dot stands for a whole word. The most insignificant object, therefore, kept to suggest something not itself may be a library. A single word book is of course a very insignificant book indeed, and the single letter, single word, single book library a still more insignificant library, but, unless you invent other words for them, they are truly book and library, and there is no more reason to invent another word for book or library in this case, than another word for animal when it is intended to include both the amoeba and man. The very simplest library consists therefore of a single recorded sign kept for use. It is the feeble faint beginning of a library but just as much a library as the New York Public Library, the Library of Congress, the British Museum, or the Bibliothèque Nationale—and the beginning of library wisdom is to seek out diligently the nature of these rudimentary libraries. § 4. _Method_ So far for definition. Now a word or two as to method. In this search for the earliest history of the making and keeping of records, library science, like all the human sciences, has at least three ways of approach or sources. The first source is history. This includes the evidence from written documents (which is direct and is history proper) and the evidence from monuments (which is circumstantial and is archaeology proper).