The dictionary is preceded by a letter addressed by Hesychius to a friend Eulogius, who is as little known as Hesychius himself. In this prefatory letter the author explains the plan and arrangement of his work, and tells us that his compilation is based upon a comprehensive lexicon of Diogenianus, but that he also availed himself of the lexicographical works of Aristarchus, Apion, Heliodorus, and others, and that he devoted himself to his task with great care and diligence. Valckenaer was the first that raised doubts respecting the genuineness of this letter in his (in Ursinus, Virgil. Collat. p. 150, &c.), and he conceived that it was the production of some later Greek, who fabricated it with a view to deceive the public and make them believe that the dictionary was his own work; but Valckenaer at the same time admits that the groundwork of the lexicon is a genuine ancient production, and only disfigured by a number of later interpolations. But a close examination of the prefatory epistle does not bring forth any thing which is at variance with the work to which it is prefixed, nor does it contain any thing to justify the opinion of Valckenaer. The investigations of Alberti and Welcker (in the Rhein. Mus. ii. pp. 269, &c., 411, &c.) have rendered it highly probable that Hesychius was a pagan, who lived towards the end of the fourth century of our era, or, as Welcker thinks, previous to A. D. 389. This view seems to be contradicted by the fact that the work also contains a number of Christian glosses and references to ecclesiastical writers, as Epiphanius and others, whence Fabricius and other critics consider Hesychius as a Christian, and identify him with the Hesychius who in the third century after Christ made a Greek translation of the Old Testament, and is often quoted by Hieronymus and others. But it is now a generally established belief that the Christian glosses and the references to Christian writers are to be considered as interpolations introduced into the work by a later hand. We may therefore acquiesce in the statement of the prefatory letter, that the work is based on a similar one by Diogenianus, and that Hesychius made further use of other special dictionaries, especially such as treated of Homeric λέξεις. There can be little doubt that the lexicon in its present form is greatly disfigured and interpolated, even setting aside the introduction of the Christian λέξεις, or glossae sacrae, as they are commonly called; but notwithstanding all this, the work is of incalculable value to us. It is now one of the most important sources of our knowledge, not only of the Greek language as such, but, to some extent, of Greek literature also; and in regard to antiquarian knowledge, it is a real storehouse of information, derived from earlier grammarians and commentators, whose works are lost and unknown. It further contains a large number of peculiar dialectical and local forms and expressions, and many quotations from other writers. The author, it is true, was more concerned about the accumulation of matter derived from the most heterogeneous sources than about a skilful and systematic arrangement ; but some of these defects are, perhaps, not to be put to the account of the original compiler, but to that of the later interpolators. This condition of the work has led some critics to the opinion, that the groundwork of the lexicon was one made by Pamphilus of Alexandria in the first century after Christ; that in the second century Diogenianus made an abridgment of it, and that at length it fell into the hands of the unknown Hesychius, by whom it was greatly interpolated, and from whom it received its present form. The interpolations must be admitted, but the rest is only an unfounded hypothesis. To restore a correct text under these circumstances is a task of the utmost difficulty.