ence. In the course of the nineteenth century a great revolution took place, not only in the economic world, but also in men's minds. Insight into the causes of social development has increased tremendously. As far back as the forties Marx and Engels showed—and from that time on every step in social science has proved it—that, in the last analysis, the history of mankind is determined, not by ideas, but by an economic development which progresses irresistibly, obedient to certain underlying laws and not to anyone's wishes or whims. In the foregoing chapters we have seen how it goes on; how it brings about new forms of production which require new forms of society; how it starts new wants among men which compel them to reflect upon their social condition, and to devise means whereby to adjust society to the new system in accordance with which production is carried on. For, we must always remember, this process of adjustment does not proceed of itself; it needs the aid of the human brain. Without thought, without ideas, there is no progress. But ideas are only the means to social development; the first impulse does not proceed from them, as was formerly believed, and as many still think; the first impulse comes from economic conditions.
Accordingly it is not the thinkers, the philosophers, who determine the trend of social progress. What the thinkers can do is to discover, to recognize, the trend; and this they can do in proportion to the clearness of their understanding of the conditions which preceded, but they can never
