rule, an economic change. Thus was the decrease and increase of crime, of suicide, and of marriages shown to be dependent on the price of corn.
Not as if, for instance, economic motives were the sole cause that marriages were made at all. Nobody would declare the sexual passion to be an economic motive. But the alteration in the annual number of marriages is called forth by changes in the economic situation.
Besides all these new sciences, there is finally to be mentioned a change in the character of the modern writing of history. The French Revolution came to the fore so clearly as a class struggle, that not only its historian must recognise that, but a number of the historians were inspired to investigate in other periods of history the rôle of the class wars, and to see in them the motive forces of human development. The classes are, however, again a product of the economic structure of society, and from this spring the antagonisms, therefore the struggles of the classes. What holds every class together, what divides them from other classes, and determines their opposition to these, are the particular class interests, a new kind of interests, of which no moralist of the eighteenth century, whatever school he might belong to, had had any idea.
With all these advances and discoveries, which certainly often enough were only piecemeal and by no means quite clear by the time of the forties in the nineteenth century, all the essential elements of the Materialist Conception of History had been supplied. They only waited for the master who should bring them under control and unify them. That was done by Engels and Marx.
Only to deep thinkers such as they were was an achievement of that nature possible. In so far that was their personal work. But no Engels, no Marx could have achieved it in the eighteenth century, before all the new sciences had produced a sufficient mass of new results. On the other hand, a man of the genius of a Kant or a Helvetius could also have discovered the Materialist Conception of History if at their time
