Distinction: Historically-informed Catholic vs. Historically-justified Catholic

There is a distinction between the Catholic who is informed of history, especially the history of his Faith, its development, its spread, its struggles, its triumphs and the Catholic who uses the particularities of history to justify adherence to belief or changes to praxis based on his whim. The latter is tied to a form of the so-called hermeneutic of discontinuity.

But this distinction is not enough because ultimately history and tradition inform the future, and actually history is full of the less-than-ideal. The Western Church has always maintained certain ideals, and I am thinking particularly with respect to liturgy and sacred music here, but these ideals have usually not been met for one reason or another.

How can we distinguish between the Catholic who wishes to respect Tradition, rooted in history, and the Catholic who takes history to reject Tradition or even argues that Tradition is fundamentally different than how it has been presently conceived and received? E.g. what if a person argues that the introduction of popular forms of folk music into liturgical music was itself somehow an organic development that began during the Protestant Reformation or even before then? Tradition, they might say, is not the upholding of Gregorian chant and Renaissance polyphony against folk influence but rather the upholding of all three (if they're being generous).

There must be some third factor. We have a third factor: the magisterium. There is and must be a certain degree to which the magisterium is anti-historicist (as opposed to anti-historical). Historical is with respect to history; historicist is with respect to historicism, which I use here as a synonym for a combination of antiquarianism and the reduction of present doctrine/praxis to particular conditions found at certain points of history. Historicism thus is the unheeded aggrandizing of any certain particular event or context and its "naturalization" into a form of Tradition and universalization (this being, of course, the deeply entrenched tendency of modernism).

The magisterium offends historicist sentimentality by crystalizing and clarifying (although not necessarily in this order) precisely what the historicist wishes to do but in a manner protected by Divine assurance. It is the historicist as it should be if only it were guided by the Holy Ghost. We may ask ourselves in the midst of historicist confusion: to whom shall we go? The magisterium hands on our Lord's "words of everlasting life," the words of Tradition as it must be properly conceived and received.

Tradition is historically informed but cannot justify itself as a historicist wishes because it transcends the whims of any individual or even group. Justification is a Pelagian fantasy attempt to appropriate God's power in oneself, an impossibility. Information, rather than being active, is receptive of form, respectful of form. 

Why do we know Gregorian chant and Renaissance polyphony are the eminent forms of music for the Roman Rite? Because the magisterium has told us so, and for the simple faithful, nothing more is needed. If only our faith were simple...