Suppose a document is intelligible. It would not be legitimate to take it into consideration without having verified its authenticity, if its authenticity has not been already settled beyond a doubt. Now in order to verify the authenticity or ascertain the origin of a document two things are required--reasoning power and knowledge. In other words, it is necessary to reason from certain positive data which represent the condensed results of previous research, which cannot be improvised, and must, therefore, be learnt. To distinguish a genuine from a spurious charter would, in fact, be often an impossible task for the best trained logician, if he were unacquainted with the practice of such and such a chancery, at such and such a date, or with the features common to all the admittedly genuine charters of a particular class. He would be obliged to do what the first scholars did--ascertain for himself, by the comparison of a great number of similar documents, what features distinguish the admittedly genuine documents from the others, before allowing himself to pronounce judgment in any special instance. Will not his task be enormously simplified if there is in existence a body of doctrine, a treasury of accumulated observations, a system of results obtained by workers who have already made, repeated, and checked the minute comparisons he would otherwise have been obliged to make for himself? This body of doctrines, observations, and results, calculated to assist the criticism of diplomas and charters, does exist; it is called Diplomatic. We shall, therefore, assign to Diplomatic, along with Epigraphy, Palæography, and Philology, the character of a subject auxiliary to historical research. Epigraphy and Palæography, Philology, and Diplomatic with its adjuncts (technical Chronology and Sphragistic) are not the only subjects of study which subserve historical research. It would be extremely injudicious to undertake to deal critically with literary documents on which no critical work has as yet been done without making oneself familiar with the results obtained by those who have already dealt critically with documents of the same class: the sum of these results forms a department to itself, which has a name--the History of Literature.[47] The critical treatment of illustrative documents, such as the productions of architecture, sculpture, and painting, objects of all kinds (arms, dress, utensils, coins, medals, armorial bearings, and so forth), presupposes a thorough acquaintance with the rules and observations which constitute Archæology properly so called and its detached branches--Numismatic and Heraldry. We are now in a position to examine to some purpose the hazy notion expressed by the phrase, "the sciences auxiliary to history." We also read of "ancillary sciences," and, in French, "sciences satellites." None of these expressions is really satisfactory.