脸上有个污点，别人见了都暗自发笑，而自己还不知道，一旦有人直言相告，马上就用手拭去。如果还说：「我脸上有污点，与你有什么关系？」就不合乎人之常情了。可是当别人指出自身的缺点错误时，人们的态度为何就不是这样呢？

相关性和因果关系之间的区别在实证工作中是根本性的。

Every improvement in the circumstances of the society tends either directly or indirectly to raise the real rent of land, to increase the real wealth of the landlord, his power of purchasing the labour, or the produce of the labour of other people.