“Good-breeding, or true politeness, is the art of showing men by external signs the internal regard we have for them. It arises from good sense, improved by good company. It must be acquired by practice and not by books.”

Source: The Love Affairs of a Bibliomaniac

Something About a Soldier (1940)

William Temple, in "Heads Designed for an Essay on Conversation" in The Works of Sir William Temple, Bart. in Four Volumes (1757), Vol. III, p. 547.
Misattributed

Source: A Memory of Light

The Pudd'nhead Maxims, preface
Following the Equator (1897)

Lecture II: Of Free Inquiry, considered as a Means for obtaining Just Knowledge
A Course of Popular Lectures (1829)
Context: However novel it may appear, I shall venture the assertion that until women assume the place in society which good sense and good feeling alike assign to them, human improvement must advance but feebly. It is in vain that we would circumscribe the power of one half of our race, and that half by far the most important and influential. If they exert it not for good they will for evil, if they advance not knowledge they will perpetuate ignorance. Let women stand where they may in the scale of improvement, their position decides that of the race.

Source: Rose in Bloom