Each one who studies ostracism deals inevitably with the problem of reasoned making into mutual agreement of contradicting testimonies. Among them are, inter alia, disagreement between Androtion and Aristotle on the problem of the date ostracism was introduced, between Philochorus and Plutarch about the meaning of number 6000 as applied to ostracism, and so on. At the present stage the task is, as far as we can judge, not so much statement of one writers' error and the other's rightness (in a lot of cases we simply have yet no possibility to estimate who is right and who is wrong), as exposing causes of disagreement, tracing the tradition under this or that evidence, if possible up to its origins. The task is certainly difficult but not always impossible to carry out, and in virtually any case such an approach leads to definite positive results.
While studying ostracism, such methods must prove to be most efficient, which are connected with complex and synthetic use of all source types in order to reconstruct integral and non-contradictory picture of events. In particular, extremely important for supplementing and correcting data of narrative tradition is analysis of other source material. We turn now to describing the latter, and first of all we should emphasize that the most significant of non-narrative sources are certainly ostraka, inscribed sherds used by Athenian citizens for voting at ostracisms.
At present more than 10000 ostraka have been discovered, although far from all of them have been properly published. Those ballots belong in all respects to most valuable sources on the theme we deal with. Information that is obtained through studying them can and must be drawn intensely and on the full scale in the course of consideration and solution of all problems relating to ostracism, as this information verifies, supplements and often corrects evidences of written tradition. Ostraka are especially useful for investigating such questions as prosopography of Athenians ostracized, means of political struggle and political propaganda at the time of ostracisms.
At the same time, when using ostraka as a source, some cautions are necessary. One should be conscious of difficulties and not yet solved (or unsolvable in principle) problems raised by that artifacts. We mean chiefly difficulties of chronological character, as for a number of reasons (first of all for insufficient clearness and reliability of applied dating criteria — archeological, paleographical, etc.) the date of many ostraka is inexact or debatable.
7. There follows the «Survey of historiography». Research works devoted specially to ostracism started to appear already in the last half of the 19 century (K. Lugebil, I. M. J. Valeton, A. Martin). In the first half of the next century several fundamental monographs on ostracism were published (J. Carcopino, A. Calderini), although by the present time they should be considered in some measure outdated. The reason lies not in shortcomings of those books, which were for their time important steps forward, but in the fact that new huge source material has appeared since their publication. We mean discoveries of ostraka that increased very much our knowledge of ostracism and must not now remain unconsidered. During last several decades almost no comprehensive monographic studies of ostracism appeared. The book by E. Vanderpool (1970) is rather popular, the monograph by R. Thomsen (1972) deals with only one specific problem (the origin of ostracism), and the book by M. Lang (1990) is not an investigation but a publication of ostraka from the Athenian Agora. As regards the most recent monograph by S. Brenne (2001), although its title includes the word «ostracism» the book in fact deals with another circle of problems (prosopography and onomastics). None of the above-mentioned books, notwithstanding all their merits, can be named a synthetic study of ostracism, a kind of new «landmark» in investigating that institution.