He thus may be said to have anticipated one of the most important truths of the modern methods of investigation: I mean that principle which lays down that just as the study of physiology should precede the study of pathology, just as the laws of disease are best discovered by the phenomena presented in health, so the method of arriving at all great social and political truths is by the investigation of those cases where development has been normal, rational and undisturbed.
The critical canon that the more a people has been interfered with, the more difficult it becomes to generalise the laws of its progress and to analyse the separate forces of its civilisation, is one the validity of which is now generally recognised by those who pretend to a scientific treatment of all history: and while we have seen that Aristotle anticipated it in a general formula, to Polybius belongs the honour of being the first to apply it explicitly in the sphere of history.
I have shown how to this great scientific historian the motive of his work was essentially the search for causes; and true to his analytical spirit he is careful to examine what a cause really is and in what part of the antecedents of any consequent it is to be looked for. To give an illustration: As regards the origin of the war with Perseus, some assigned as causes the expulsion of Abrupolis by Perseus, the expedition of the latter to Delphi, the plot against Eumenes and the seizure of the ambassadors in Bœotia; of these incidents the two former, Polybius points out, were merely the pretexts, the two latter merely the occasions of the war. The war was really a legacy left to Perseus by his father, who was determined to fight it out with Rome. [78]
Here as elsewhere he is not originating any new idea. Thucydides had pointed out the difference between the real and the alleged cause, and the Aristotelian dictum about revolutions, οὐ περὶ μικρῶν ἀλλ’ ἐκ μικρῶν, draws the distinction between cause and occasion with the brilliancy of an epigram. But the explicit and rational investigation of the difference between αἰτία, ἀρχὴ, and πρόφασις was reserved for Polybius. No canon of historical criticism can be said to be of more real value than that involved in this distinction, and the overlooking of it has filled our histories with the contemptible accounts of the intrigues of courtiers and of kings and the petty plottings of backstairs influence—particulars interesting, no doubt, to those who would ascribe the Reformation to Anne Boleyn’s pretty face, the Persian war to the influence of a doctor or a curtain-lecture from Atossa, or the French Revolution to Madame de Maintenon, but without any value for those who aim at any scientific treatment of history.
But the question of method, to which I am compelled always to return, is not yet exhausted. There is another aspect in which it may be regarded, and I shall now proceed to treat of it.
One of the greatest difficulties with which the modern historian has to contend is the enormous complexity of the facts which come under his notice: D’Alembert’s suggestion that at the end of every century a selection of facts should be made and the rest burned (if it was really intended seriously) could not, of course, be entertained for a moment. A problem loses all its value when it becomes simplified, and the world would be all the poorer if the Sibyl of History burned her volumes. Besides, as Gibbon pointed out, ‘a Montesquieu will detect in the most insignificant fact relations which the vulgar overlook.’
Nor can the scientific investigator of history isolate the particular elements, which he desires to examine, from disturbing and extraneous causes, as the experimental chemist can do (though sometimes, as in the case of lunatic asylums and prisons, he is enabled to observe phenomena in a certain degree of isolation). So he is compelled either to use the deductive mode of arguing from general laws or to employ the method of abstraction, which gives a fictitious isolation to phenomena never so isolated in actual existence. And this is exactly what Polybius has done as well as Thucydides. For, as has been well remarked, there is in the works of these two writers a certain plastic unity of type and motive; whatever they write is penetrated through and through with a specific quality, a singleness and concentration of purpose, which we may contrast with the more comprehensive width as manifested not merely in the modern mind, but also in Herodotus. Thucydides, regarding society as influenced entirely by political motives, took no account of forces of a different nature, and consequently his results, like those of most modern political economists, have to be modified largely [81] before they come to correspond with what we know was the actual state of fact. Similarly, Polybius will deal only with those forces which tended to bring the civilised world under the dominion of Rome (ix. 1), and in the Thucydidean spirit points out the want of picturesqueness and romance in his pages which is the result of the abstract method (τὸ μονοειδὲς τῆς συντάξεως) being careful also to tell us that his rejection of all other forces is essentially deliberate and the result of a preconceived theory and by no means due to carelessness of any kind.
Now, of the general value of the abstract method and the legality of its employment in the sphere of history, this is perhaps not the suitable occasion for any discussion. It is, however, in all ways worthy of note that Polybius is not merely conscious of, but dwells with particular weight on, the fact which is usually urged as the strongest objection to the employment of the abstract method—I mean the conception of a society as a sort of human organism whose parts are indissolubly connected with one another and all affected when one member is in any way agitated. This conception of the organic nature of society appears first in Plato and Aristotle, who apply it to cities. Polybius, as his wont is, expands it to be a general characteristic of all history. It is an idea of the very highest importance, especially to a man like Polybius whose thoughts are continually turned towards the essential unity of history and the impossibility of isolation.
Farther, as regards the particular method of investigating that group of phenomena obtained for him by the abstract method, he will adopt, he tells us, neither the purely deductive nor the purely inductive mode but the union of both. In other words, he formally adopts that method of analysis upon the importance of which I have dwelt before.
And lastly, while, without doubt, enormous simplicity in the elements under consideration is the result of the employment of the abstract method, even within the limit thus obtained a certain selection must be made, and a selection involves a theory. For the facts of life cannot be tabulated with as great an ease as the colours of birds and insects can be tabulated. Now, Polybius points out that those phenomena particularly are to be dwelt on which may serve as a παράδειγμα or sample, and show the character of the tendencies of the age as clearly as ‘a single drop from a full cask will be enough to disclose the nature of the whole contents.’ This recognition of the importance of single facts, not in themselves but because of the spirit they represent, is extremely scientific; for we know that from the single bone, or tooth even, the anatomist can recreate entirely the skeleton of the primeval horse, and the botanist tell the character of the flora and fauna of a district from a single specimen.