The tragedy of 'Humanae Vitae' is that in an otherwise beautiful meditation on marriage, Pope Paul got bogged down by one sentence: "Each and every act ..."  Unfortunately, Paul yielded to the worst possible argument against the report of the Commission: that modifying the traditional teaching would weaken the teaching authority of the church, and specifically of the pope.  We know that the argument had it precisely backwards: the failure to respond to new information and new insights (and the hardline subsequently adopted by Pope John Paul II) is what caused a massive erosion in the church's credibility to teach about marriage, sex and family.