respect of each fact derived from such a tradition we must ask whether it has not been distorted by the interest, the vanity, or the prejudices of the group concerned. We may even ignore the author, and ask whether there was anything likely to make for or against correct observation, common to all the men of the time and country in which the observation must have been made: for example, what means of information, and what prejudices, had the Greeks of Herodotus' time with respect to the Scythians.
The most useful of all these general inquiries has reference to that mode of transmitting anonymous statements which is called tradition. No second-hand statement has any value except in so far as it reproduces its source; every addition is an alteration, and ought to be eliminated. Similarly, all the intermediary sources are valueless except as copies of the original statement founded directly on observation. The critic needs to know whether this transmission from hand to hand has preserved or distorted the original statement; above all, whether the tradition embodied in the document was written or oral. Writing fixes a statement, and ensures its being transmitted faithfully; when a statement is communicated orally, the impression in the mind of the hearer is apt to be modified by confusion with other impressions; in passing from one intermediary to another the statement is modified at every step, and as these modifications arise from different causes, there is no possibility of measuring or correcting them.
Oral tradition is by its nature a process of continual alteration; hence in the established sciences only written transmission is accepted. Historians have no avowable motive for proceeding differently, at any rate when it is a