That is an expression familiar to many and often found in the writings of many scholars, scientists and philosophers, and of those commentators who, by their reasonings or by their combinations, add a little to simple historic narration and utilize this opinion as an hypothesis to find a starting point in the immense mass of human facts, which, at first sight and after first examination, appear so confused and irreducible. This belief, this current opinion, has become for reasoning historians, or even for rationalists, a semi-doctrine, which has recently been urged several times, as a decisive argument, against the unitary theory of the materialistic conception. And indeed, this belief is so deeply rooted and this opinion so widespread, of history being only intelligible as the juncture and the meeting of various factors, that, in consequence, many of those who speak of social materialism, whether they be its partisans or adversaries, believe that they save themselves from embarrassment by affirming that this whole doctrine consists in the fact that it attributes the preponderance or the decisive action to the _economic factor_. It is very important to take account of the fashion in which this belief, this opinion, or this semi-doctrine takes its rise, because real and fruitful criticism consists principally in knowing and understanding the motive of what we declare an error. It does not suffice to reject an opinion by characterizing it as false doctrine. Error always arises from some ill-understood side of an incomplete experience, or from some subjective imperfection. It does not suffice to reject the error; we must overcome it, explain it and outgrow it. Every historian, at the beginning of his work, performs, so to speak, an act of elimination. First, he makes erasures, as it were, in a continuous series of events; then he dispenses with numerous and varied suppositions and precedents; more than this, he tears up and decomposes a complicated tissue. Thus, to begin with, he must fix a point, a line, a boundary, as he chooses; he must say, for example: I wish to relate the beginning of the war between the Greeks and the Persians, or to inquire how Louis XVI. was brought to convene the States General. The narrator finds himself, in a word, confronted with a _complexus_ of accomplished facts and of facts on the point of being produced, which in their totality present a certain aspect. Upon the attitude which he takes depends the form and the style of every narration, because to compose it he must take his point of departure from things already accomplished, in order to see henceforth how they have continued to develop.