The Most Reverend John F. Donoghue, Archbishop of Atlanta, writes on proportionate reasons.
The Church holds her members to acceptance, complete acceptance of her teaching on matters of faith and morals. We can argue incessantly about degrees of authority, and types of authoritative statement. But the Church's teaching is to be held and practiced. In moral theology, there are two kinds of cooperation involved in this question, and they break down as follows: 'Formal cooperation is that degree of cooperation in which my will embraces the evil object of another's will. Thus, to vote for a candidate because he favors abortion is formal cooperation in his evil political acts. However, to vote for someone in order to limit a greater evil, that is, to restrict in so far as possible the evil that another candidate might do if elected, is to have a good purpose in voting. The voter's will has as its object this limitation of evil and not the evil which the imperfect politician might do in his less than perfect adherence to Catholic moral principles. Such cooperation is called material, and is permitted for a serious reason, such as preventing the election of a worse candidate.'