Anscombe used this distinction to draw a line between natural and artificial methods of contraception. A married couple that chooses to make love at a time when they can predict that there will be no pregnancy may still be performing an act of a reproductive kind. (Most acts of that kind will produce no children, just as most acorns don't produce oaks.) It doesn't alter what they are doing then that they may plan to abstain at other times. But if they take steps to make infertile an act that would otherwise be fertile, they alter the nature of the act, which ceases to be in place in, and only in, marriage. In either case, they may have a further intention that is innocent or even commendable: say, not to have more children than they can support. Yet it makes an ethical difference how they achieve that.

In the years after Humanae Vitae (1968), Anscombe was often invited to speak against contraception. Mary Geach notes that she was not just defending the party line but taking a position in which she never wavered even when, for a time, it appeared that the Church might change its mind. Yet it is regrettable that its prominence may distract attention, or attract disbelief, in relation to other issues where there is better reason to suppose that such a distinction defines not just a value but a requirement. (Intercourse that is open to reproduction may in that respect be best without alone being licit.) Those who find Anscombe's heroic obduracy misplaced here should turn their attention to an area of debate where it found an appropriate home. In 1956, the University of Oxford proposed that Harry Truman, the victor of Hiroshima and Nagasaki, be given an honorary degree. When Anscombe made a formal protest at a meeting of Congregation, she found herself in a minority of four - Oxford dons en masse being as foolish as any other mass of men. (However, her concluding words, which expressed a fear that the ensuing encænia might see the end of God's patience, could not have weighed with most of her audience.)

Her disapproval of Truman connects again with her concern about intentionality. In a early piece titled The Justice of the Present War Examined, published in 1939 to justify conscientious objection to our involvement in the Second World War, she permitted the accidental killing of civilians through military action, even if it is predictable (so long as the total effects are good). What she could not condone was making a group of persons, including civilians, a target in order, by attacking them all, to attack some members of the group whom it is legitimate to target. A later example was this: "The British wanted to destroy some German soldiers on a Dutch island in the Second World War, and chose to accomplish this by bombing the dykes and drowning everybody. (The Dutch were their allies.)" Such an agent murders some men himself in the hope, no doubt, of preventing other deaths. But the Ten Commandments tell each of us what to do or omit oneself. It is not one's task to play God, and hazard guesses about alternative narratives in which the Commandments are broken more or less often. One's duty is to keep God's word, not to act so as to minimise infringements by oneself or others - a causal notion that is deeply problematic.