I've read a few articles and blogs where an appeal to Catechism 2309 has been made as an explanation as to why (for example) the US President is the one who should make the prudential decision as to when a war should be undertaken. It seems to me that it is a mistake to think things are quite so clear cut.

Firstly, the Catechism does not point to any single individual, nor to any single group, but says that the decision belongs to "those who have responsibility for the common good". We have to then inquire as to what the "common good" is, and who is given responsibility for it.

The Catechism has a section which discusses the common good. This section identifies what it is ("the sum total of social conditions which allow people, either as groups or as individuals, to reach their fulfillment more fully and more easily"), and who has responsibility for it:

"The common good concerns the life of all. It calls for prudence from each, and even more from those who exercise the office of authority."

So, although those with an authoritative office (such as the President) do clearly have a particularly strong responsibility for the common good, it is not something which rests solely within such an office. It calls for prudence from each of us.

Prudence is clearly needed not only from such as the President, but also from Congress, the Courts, the media, the military and intelligence agencies, and a wide range of other groups, who must always share in the responsibility for a war. This must necessarily include the Bishops and the Pope.

And this extends down to each individual. Another part of the Catechism indicates that "the citizen is obliged in conscience not to follow the directives of civil authorities when they are contrary to the demands of the moral order, to the fundamental rights of persons or the teachings of the Gospel".

So, each of us is responsible for the common good, and each has to at least concur that we are not being directed to do something immoral. The Catechism does not place responsibility in a single individual.