In order that the conclusion may be certain, two conditions are necessary.
(1) The general proposition must be accurately true; the two facts which it declares to be connected must be connected in such a way that the one is never found without the other. If this condition were completely satisfied we should have a law, in the scientific sense of the word; but in dealing with the facts of humanity—apart from those physical conditions whose laws are established by the regular sciences—we can only work with empirical laws obtained by rough determinations of general facts which are not analysed in such a manner as to educe their true causes. These empirical laws are approximately true only when they relate to a numerous body of facts, for we can never quite know how far each is necessary to produce the result. The proposition relating to the language of the name of a city does not go enough into detail to be always true. Petersburg is a German name, Syracuse in America bears a Greek name. Other conditions must be fulfilled before we can be sure that the name is connected with the nationality of the founders. We should, therefore, only employ such propositions as go into detail.
(2) In order to employ a general proposition which goes into detail, we must have a detailed knowledge of the particular fact; for it is not till after this fact has been established that we look for an empirical general law on which to found an argument. We shall begin, then, by studying the particular conditions of the case (the situation of Salamis, the habits of the Greeks and Phœnicians); we shall not work on a single detail, but on an assemblage of details.
Thus, in historical reasoning it is necessary to have (1) an accurate general proposition; (2) a detailed knowledge of a past fact. It is bad workmanship to assume a false general proposition—to suppose, for example, as Augustin Thierry did, that every aristocracy had its origin in a conquest. It is bad workmanship, again, to found an argument on an isolated detail (the name of a city). The nature of these errors indicates the precautions to be taken.
(1) The spontaneous tendency is to take as a basis of reasoning those "common-sense truths" which form nearly the whole of our knowledge of social life. Now, the greater part of these are to some extent false, for the science of social life is still imperfect. And the chief danger in them lies in the circumstance that we use them unconsciously. The safest precaution will be always to formulate the supposed law on which we propose to base an argument. In every instance where such and such a fact occurs, it is certain that such and such another fact occurs also. If this proposition is obviously false, we shall at once see it to be so; if it is too general, we shall inquire what new conditions may be introduced to make it accurate.
(2) A second spontaneous impulse leads us to draw consequences from isolated facts, even of the slightest kind (or rather, the idea of each fact awakens in us, by association, the idea of other facts). This is the natural procedure in the history of literature. Each circumstance in the life of an author supplies material for reasoning; we construct by conjecture all the influences which could have acted upon him, and we assume that they did act upon him. All the branches of history which study a single species of facts, isolated from every other species (language, arts, private law, religion), are exposed to the same danger, because they deal with fragments of human life, not with comprehensive collections of phenomena. But few conclusions are firmly established except those which rest on a comprehensive body of data. We do not make a diagnosis from a single symptom, but from a number of concurrent symptoms. The precaution to be taken will be to avoid working with an isolated detail or an abstract fact. We must have before our minds actual men, as affected by the principal conditions under which they lived.
We must be prepared to realise but rarely the conditions of a certain inference; we are too little acquainted with the laws of social life, and too seldom know the precise details of an historical fact. Thus most of our reasonings will only afford presumptions, not certainties. But it is with reasonings as with documents.[202] When several presumptions all point in the same direction they confirm each other, and end by producing a legitimate certitude. History fills up some of its gaps by an accumulation of reasonings. Doubts remain as to the Phœnician origin of various Greek cities, but there is no doubt about the presence of the Phœnicians in Greece.
CHAPTER IV
THE CONSTRUCTION OF GENERAL FORMULÆ
I. Suppose we had methodically arranged all the historical facts established by the analysis of documents, or by reasoning; we should possess a systematised inventory of the whole of history, and the work of construction would be complete. Ought history to stop at this point? The question is warmly debated, and we cannot avoid giving an answer, for it is a question with a practical bearing.