Paul Inwood has initiated an interesting discussion at Pray Tell about the repeated calls by the Magisterium of the Church for Chant to be 'restored' to a place of primacy in Church music, especially at Mass. These calls, he says, indicate that it has been a very long time since chant was the 'norm' at Mass.
He gathers a useful set of quotations from official documents, but reads them in an odd way. The more they say that Chant should be given pride of place, the more he thinks that Chant does not have pride of place, because if it it did they would not need to insist on it so much. One confusion here is that, as Ben Whitworth of the Orkney Schola points out in the comments, he fails to distinguish what is NORMATIVE from what is NORMAL. Chant is the norm, and has been the norm; that is not a statistical claim but a rule and a value-judgement. Tra la sollicitudini and Guéranger, when they called for the restoration of chant, were re-articulating a norm of Catholic worship which had forgotten by all too many.
There are many such norms today...
But another confusion in Inwood's post is his identification of 'chant' with the authentic chant melodies of the Graduale Romanum. He points out that the Ratisbon ('Pustet') Gradule in use until the Graduale Romanum of 1907, and Pustet's predecessors going back to the Rennaisance, were simplified (or 'bastardised', as he calls them). We can't blame people for not using an edition which had not yet been printed, however: before 1907 there was no 1907 edition, well, obviously! And for all its deficiencies, the Pustet edition was (a) recognisably Chant, and (b) widely used. So Inwood's claim that chant settings were not widely used before the Solemnes restoration simply falls on its face.
Similarly, he dismisses the simplified versions of the chant settings used later. He doesn't name it, but the 'Rossini' propers are the obvious example of this in the English-speaking world; they set all the propers of the year to psalm-tones. Their use to the exclusion of the authentic (or indeed simplified) Gregorian melodies is of course very regrettable. But it is still chant.
Chant was normative at the eve of the Second Vatican Council in a very practical way: in accordance with the magisterial documents, it was being taught in Catholic schools, and the places where the liturgy was being celebrated with full splendour, such as monasteries and cathedrals, chant was being sung with the best available editions and to a high standard. In other places this may not have been possible, any more than the normative form of the Mass - Missa Solemnis, with priest, deacon, and subdeacon - could not always be celebrated in small parishes. But even today, when chant has almost disappeared from Catholic liturgical life, outside of the Traditional Mass, it is still normative for Catholic liturgy, for theological and aesthetic reasons, and this normative role is respected by those musicians and composers who try to use chant in the liturgy and who use chant as an inspiration. And it is being flouted by those who do the opposite.