Letter 3 — On True and False Friendship (§2)

“Now if you used this word of ours in the popular sense, and called him “friend” in the same way in which we speak of all candidates for election as “honourable gentlemen,” and as we greet all men whom we meet casually, if their names slip us for the moment, with the salutation “my dear sir,”—so be it. But if you consider any man a friend whom you do not trust as you trust yourself, you are mightily mistaken and you do not sufficiently understand what true friendship means.”