We can conceive a more concrete method which, instead of comparing fragments, should compare wholes, that is entire societies, either the same society at different stages of its evolution (England in the sixteenth, and again in the nineteenth century), or else the general evolution of several societies, contemporary with each other (England and France), or existing at different epochs (Rome and England). Such a method might be useful negatively, for the purpose of ascertaining that a given fact is not the necessary effect of another, since they are not always found together (for example, the emancipation of women and Christianity). But positive results are hardly to be expected of it, for the concomitance of two facts in several series does not show whether one is the cause of the other, or whether both are joint effects of a single cause. The methodical investigation of the causes of a fact requires an analysis of the conditions under which the fact occurs, performed so as to isolate the necessary condition which is its cause; it presupposes, therefore, the complete knowledge of these conditions. But this is precisely what we never have in history. We must therefore renounce the idea of arriving at causes by direct methods such as are used in the other sciences. As a matter of fact, however, historians often do employ the notion of cause, which, as we have shown above, is indispensable for the purpose of formulating events and constructing periods. They know causes partly from the authors of documents who observed the facts, partly from the analogy of the causes which we all observe at the present day. The whole history of events is a chain of obviously and incontrovertibly connected incidents, each one of which is the determining cause of another. The lance-thrust of Montgomery is the cause of the death of Henry II.; this death is the cause of the accession to power of the Guises, which again is the cause of the rising of the Protestants. The observation of causes by the authors of documents is limited to the interconnection of the accidental facts observed by them; these are, in truth, the causes which are known with the greatest certainty. Thus history, unlike the other sciences, is better able to ascertain the causes of particular incidents than those of general transformations, for the work is found already done in the documents. In the investigation of the causes of general facts, historical construction is reduced to the analogy between the past and the present. Whatever chance there is of finding the causes which explain the evolution of past societies must lie in the direct observation of the transformations of present societies. This is a branch of study which is not yet firmly established; here we can only state the principles of it.