I seem to remember there was a medieval philosopher--maybe Russell mentions him in his History of Western Philosophy--who talked about peer influence or what a social scientist today might call regression toward the mean. He advised that, to live a saintly life, one should surround oneself with saintly people. Who was he? Did he write anything available today? Any pithy quotes?

Blaise Pascal, though not a medieval philosopher but an early modern one, did recognize that his famous wager was not always sufficient to cause an unbeliever to believe. Thus he recommends spending time with believers, performing the rituals with them, and, eventually, one would come to believe. He says:

"You would like to attain faith and do not know the way; you would like to cure yourself of unbelief and ask the remedy for it. Learn of those who have been bound like you, and who now stake all their possessions. These are people who know the way which you would follow, and who are cured of an ill of which you would be cured. Follow the way by which they began; by acting as if they believed, taking the holy water, having masses said, etc. Even this will naturally make you believe, and deaden your acuteness. "But this is what I am afraid of." And why? What have you to lose?" (Pascal, Blaise, 1670, Pensées, translated by W. F. Trotter, London: Dent, 1910; #233)

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