Many people -- including well-catechized Catholics -- believe that the doctrines of the Catholic Church constitute a monolithic-type entity which offers no room for disagreement. This is not the case.
The Catholic Church has always had a number of varying theological systems co-existing within its bounds of orthodoxy. The most famous example is probably the 16th and 17th century dispute De Auxiliis, in which Dominicans and Jesuits (strongly) disagreed over the relationship between free will and grace. In the end, the pope stated that that the positions of both camps could be held within the Catholic Church, and he ordered both sides to stop claiming that the others were heretical. Yet this is not the only example of theological pluralism within the Catholic Church. The high and late middle ages were full of various theological schools and systems which disagreed on various points -- for example, the Thomists, the Scotists, and later, the Ockhamists -- yet were all held as legitimate theological options for Catholics to hold. Pluralism can be found even earlier, though: in the early Church, the schools of Antioch and Alexandria each articulated their Christologies in ways which greatly differed, yet which were nonetheless valid options for members of the Church (apart from the various condemned heresies arising from each school, of course).
Note that I am not saying that one is free to disagree with the Church -- where the Church has specifically defined a doctrine or its limits, we must give our assent. But there are innumberable theological topics on which orthodox Catholics can formulate differing explanations, provided that they remain within the bounds of orthodoxy as defined by the Magisterium.
There is a very contemporary -- and for some, controversial -- example of theological pluralism as well.
On October 31st, 1999, authoritative representatives of the Lutheran World Federation and of Pope John Paul II met in Wittenburg, Germany to sign the Joint Declaration on the Doctrine of Justification. Along with the Common Statement and Annex, the JDDJ states the following about the degree of agreement found:
- 40. The understanding of the doctrine of justification set forth in this Declaration shows that a consensus in basic truths of the doctrine of justification exists between Lutherans and Catholics. In light of this consensus the remaining differences of language, theological elaboration, and emphasis in the understanding of justification described in paras. 18 to 39 are acceptable. Therefore the Lutheran and the Catholic explications of justification are in their difference open to one another and do not destroy the consensus regarding the basic truths.