This paper discusses the question of consistency between theoretical premises and narrative practice in Histories of Polybius, the Greek historian who has been numbered together with his predecessor Thucydides in the top class of ancient historiography. For, while modelling Thucydides in setting the purpose of historical research and writing for providing practical lessons for future men of state-affairs (pragmata), he advanced further in formulating the methodological principles and the requirements for would-be historian. Thus, he was the first to conceptualize the pragmatike historia, and has been duly acknowledged as such.
The second chapter of this paper attempts to exhibit the cardinal aspects of the pragmatike historia. According to the historian, the genre of history he chose to write is different from that of the so-called genealogike historia: while Polybius himself does record mostly what he has seen and heard in person, thus likelier to be more faithful to the historical truth, the latter, usually tracing back to the remote past far beyond historian's ken, thus unavoidably dependent upon what has been transmitted through the writings of predecessors, by and large regardless of the truth. And Polybius tries to expound the methodology of research to the readers, as occasions are given throughout Histories. apodeiksis and aitiologia are its key-words: the former signifies the principle of analytically demonstrating facts by means of various evidences and testimony, the latter the causative explanation of historical events. The famous analysis of the Roman constitution and the military system as the secrets of Rome's success Polybius presents in the book VI of Histories epitomizes his rationalistic approach to history. And the confidence in human knowledge's continuous expansion his contemporaries are witnessing particularly in the field of ecumenical geography, reflects the historian's rationalism in a way very much reminiscent of the 18th century's European intellectual optimism.
Yet, does the narrative of Histories abide by the methodological principles? The third chapter answers to this question by testing one of the most prominent features of Polybius' narrative, namely the use of the term tyche. (the total appearance is 137 times) That the historian makes frequent recourses to it prima facie contradicts diametrically the conclusion just drawn in the previous chapter, for usual connotations of the term (chance, fortune, and fate) seemingly do replace, rather than supplement, the rational causation of events. The author of this paper firstly proposes classify the usage of tyche in Histories into three categories: etiological tyche, moral (or punitive) tyche, and teleological (or providential) tyche. As for the etiological tyche, there is no need to further our discussion, for the historian himself concedes its indispensability due to human perception's limitation in cases where natural elements affect or multiple factors converge to produce historical circumstance beyond the expectation of historical agents.
In the meantime, the remaining two categories are a different matter, if they are meant to be significant as of more than a conventional way of expression. For their premise is that a transcendental power intervenes in human affairs to punish the moral deviant or, to speak tyche operating on a far grander scale, to lead the entire oikumene according to a predestined plan (for example, a cycle of rise and fall). However, the final analysis of the concrete ways the historian refers to tyche, whether moral or providential, shows that the reference of tyche are nothing but a rhetorical and convenient way of expression. That moral tyche can't be by any means an objective force affecting human actions is revealed by its inconsistent nature. That is, the historian applies the operation of moral tyche solely to the figures alleged to be villains, while representing as outstanding exceptions to the rule his heroes or favorites such as Aemilius Paullus, Scipio Aemilianus (protagonists of the Roman imperialism as well as personal patrons during his stay at Rome), Syracusan tyrant Hiero (one of his ideal Hellenistic monarchs), and Philopoemen (his senior compatriot of same political alignment).
Finally, providential tyche appearing in a few prominent places are best to interpreted to refer to the macroscopic trend that becomes clearer to the intuitive perception of historian only when he attempts to put together in an organic whole the discrete parts of the world. Thus, according to the conventional way of expression of his days, Polybius speaks of tyche instead of the grand course of history that he himself intuitively grasps, as when he says as follows in the famous locus (VIII, 2, 3-6): "For how by the bare reading of events in Sicily or in Spain can we hope to learn and understand either the magnitude of the occurrence s or what form of government tyche has employed to accomplish the most surprising feat she has performed in our times, that is to bring the known parts of the oikumene under one rule and dominion, a thing absolutely without precedent?"
Thus, we may after all conclude that Polybius is by and large consistently rationalistic in theory and practice of historiography, thus preempting some significant features of modern historical science.