A long time is necessary for ideas to establish themselves in the minds of crowds, but just as long a time is needed for them to be eradicated. For this reason crowds, as far as ideas are concerned, are always several generations behind learned men and philosophers. All statesmen are well aware to-day of the admixture of error contained in the fundamental ideas I referred to a short while back, but as the infiuence of these ideas is still very powerful they are obliged to govern in accordance with principles in the truth of which they have ceased to believe.