But in this apparent movement, there are the elements of a more exact view. These concurrent factors, which abstract thought conceives and then isolates, have never been seen acting each for itself. On the contrary, they act in such a manner that it gives birth to the concept of reciprocal action. Moreover, these factors themselves arise at a given moment, and it is not until later that they acquired that physiognomy which they have in the particular narration. This State, it is well known, arose at a given moment. As for every rule of law, it may either be remembered or conjectured that it went into effect under such or such circumstances. As for many customs, it may be remembered that they were introduced at a given moment; and the simplest comparisons of the facts in different times or different places would show how society, as a whole, and in its character of being an aggregation of different classes, had taken and took continuously various forms. The reciprocal action of the different factors, without which not even the simplest narration would be possible, like the more or less exact information upon the origins and the variations of the factors themselves, called for research and thought more than did the constructive narration of those great historians who are real artists. And, in effect, the problems which arise spontaneously from the data of history, combined with other theoretical elements, gave birth to the different so-called practical disciplines, which in a more or less rapid fashion and with varying success, have developed from the ancients up to our days, from ethics to the philosophy of law, from politics to sociology, from law to economics.