Before entering into a description of the early history of Japan, it may be of some service to the foreign reader to learn when the authentic history of Japan begins. Generally it is not an easy matter to draw a distinct line of demarcation between the historic and the prehistoric age in the history of any country, and in order to get rid of this difficulty, an intermediate age called the proto-historic was invented by modern scholars, and has been in vogue up to now. It is true that, by making use of this term, one aim was surely attained, but two difficulties were thereby created in lieu of one dismissed. We were freed, indeed from the hard task of making a delicate discrimination between the historic and the prehistoric age, but at the same time we took up the burden of distinguishing the proto-historic age from both the historic and the prehistoric! And these new difficulties cannot be said to be easier to meet than the old, so that it may be doubted whether it was wise to intercalate the proto-historic age between the two, if the promotion of scientific exactitude was the main purpose of such an intercalation. A polygon, however the number of its sides be augmented, can never make a circle in the exact sense. I shall not, therefore, try to adhere scrupulously to the above-mentioned threefold division in discharging the task which I have undertaken. Let me turn then to the line of demarcation between the historic and the prehistoric age without troubling myself about the proto-historic. This line must be drawn by first making clear the signification of the historic age, and not by defining the term "prehistoric." What, then is the historic age? It may be defined as an age, the authentic history of which can, in a large measure, be ascertained, or as an age which has an historical record, contemporary and fairly reliable. It is to be regretted that we cannot dispense with such precautionary expressions as 'to a large measure' and 'fairly', but we cannot avoid retaining them, and therein lies the true difficulty of making an exact demarcation. Moreover, an age, the history of which was regarded at one time as impossible of being ascertained, often may become ascertainable as the result of ever-increasing discoveries of new materials as well as of the new methods of their deciphering. In other words, the demarcation, however conscientiously made at one time, is liable to be shifting, and the reason for the demarcation gradually changes _pari passu_. As the word prehistoric has now begun to be used independently of 'historic', the historic age may be better defined as an age which has a civilisation advanced enough to have a record of its own. So far a country may be said to be in an historic age, even at an epoch the historical sources of which are considered not to be extant anywhere, only if the standard of civilisation be high enough for that. Unless we adopt this definition, the line of demarcation may shift more and more