Hierarchy of truths and analogy of faithHave you ever heard anyone use the idea of the hierarchy of truths to dismiss a teaching they didn't like because it is "low" on the hierarchy of truths? The hierarchy of truths is mentioned in Vatican II. “When comparing doctrines with one another, they [theologians] should remember that in Catholic doctrine there exists a ‘hierarchy’ of truths, since they vary in their relation to the fundamental Christian faith” (UR, no. 11). As Doug Bushman points out, it is connected to the analogy of faith. The Catechism says "Be attentive to the analogy of faith. By 'analogy of faith' we mean the coherence of the truths of faith among themselves and within the whole plan of Revelation. " (114)
The truths of the faith have the same characteristics of any analogy. First of all, although they seem to be about disperate things, they are all in some way related to each other and maintain a fundamental underlying unity. In other words, their diversity is a diversity in unity. Second, there are primary and secondary truths. Just as in an analogy there is a proper meaning and a derivative meaning of a word, so the truths of the faith are arranged in a hierarchy of truths, some being more fundamental, others being dependent on the fundamental ones. For instance, the teaching on the Immaculate Conception of Mary is dependent on the teaching of the redemptive grace of the Cross.
Some people try to use the hierarchy of truths in order to marginalize and make less important some of the more derivative truths. In other words, if some teaching of the Church is "way down" on the hierarchy of truths, they'll feel more free to ignore it or consider it expendible. This is what a lot of people do, for instance, with the teaching on contraception. "Well, its okay to ignore it. I mean, its not like I'm denying the Trinity or anything."
This is not what the hierarchy of truths means, however. The derivative truths are no less "important" than the fundamental ones. But they can only be understood in the context of the fundamental ones. For instance, one cannot reject the Immaculate Conception of Mary and remain a Catholic. It is in a way just as important a teaching.