Quotes from the printed lectures of Professor Ralph Barton Perry
The absurdities of yesterday are the common sense of today; the common sense of yesterday is now obsolete and quaint. The crank [an eccentric person, especially one who is obsessed by a particular subject or theory] of the sixteenth century was the man who said that the earth moved; the crank of the twentieth century is the man who says that it does not. Moreover, once common sense is thus reflected upon, it is seen to be in part, at least, the result of wholly irrational forces , such as habit and imitation.
Unless you were an extraordinary child you were very curious about what you called the world; curious as to who or what made it, why it was made, how it was made, why it was made as it is, and what it is like in those remote and dim regions beyond the range of your senses. Then you grew up, and having grown up, you acquired common sense, or rather common sense acquired you. […] common sense appears not as the illumination of mature years, but rather as a hardening of the mind, the worldliness and complacency of a life immersed in affairs.
[Socrates] found men busy, to be sure, but strangely unaware of what they were about; they felt sure they were getting somewhere, but they did not know where.