A single reference, found in one author, to the works of another, who, in his turn, needs the same kind of authentication, may seem to be a fallacious, or insufficient, and obscure kind of proof; for this reference or this quotation may possibly be an interpolation; or the reference may be of too slight or indefinite a kind to make it certain, that the work now extant is the same as that so referred to. In truth, the validity of this kind of proof arises from its _amount_, from its _multifariousness_, and from its _incidental character_. For although a single and solitary testimony may be inconclusive, many hundred independent testimonies, all bearing upon the same point, are much more than sufficient to remove every shadow of doubt; some of these references may be slight and indefinite, but others are full, particular, and complete. If some are formal and direct, and such therefore as might be supposed to have been inserted with a fraudulent design, others are altogether circuitous and purely incidental. If some have descended to us through the same channels, others are derived from sources as far removed as can be imagined from the possibility of collusion. But a work may happen to want this kind of evidence, and yet, on other grounds, it may possess a valid claim to genuineness. In fact, almost all the existing remains of ancient literature are abundantly authenticated by the numerous and explicit quotations from them, or descriptions of them, that occur in other works. And there are very few books that do not contain some direct or some indirect allusions to other works: so it is that the remains of ancient literature, taken as a mass, contains within itself the proof of the authenticity of each part. The nature of the case gives to this body of references a pyramidal form. In the most remote age it is, of course, small in amount; in the next age it becomes much more ample and substantial; and in later periods, it spreads itself over the entire surface of literature. The literature of the Greeks was national and original; they borrowed from their neighbours less in poetry, philosophy, and history, than in religion, or the arts: their _early_ writers were not, in the modern sense of the term, men of learning; their works were composed at the impulse of genius, and of the moving spirit of the times. The habit of literary allusion and quotation had not then been formed, nor indeed was it congruous with this order of intellectual production; and yet the early Greek writers contain mutual references, which, if not numerous, are sufficient to establish and ascertain, in most instances, the genuineness of each.