http://www.slate.com/toolbar.aspx?action=print&id=2267847 Vast moral revolutions do take place once in a while, but it is hard to figure out exactly what sets them into motion or brings them to success. A high-minded prophet in some part of the world denounces an old and dreadful social custom. A smattering of do-gooders plead for reform. The reform in question appears, at a glance, to be impractical, unpopular, and unlikely. And yet enormous masses of people somehow—but how?—end up suddenly embracing the revolutionary idea, and they bend to the task of digging a new foundation for the whole of society. The improbable reform, upon completion, turns out to be irreversible. And in retrospect, absolutely everyone, or nearly so, solemnly agrees that good has, in fact, been done, and moral progress on the grandest of scales is more than a figment of the wistful and naive imagination.