Council of Trent: Session XXI, Communion, Chapter II

CHAPTER II. The power of the Church as regards the dispensation of the Sacrament of the Eucharist.

It furthermore declares, that this power has ever been in the Church, that, in the dispensation of the sacraments, their substance being untouched, it may ordain,--or change, what things soever it may judge most expedient, for the profit of those who receive, or for the veneration of the said sacraments, according to the difference of circumstances, times, and places. And this the Apostle seems not obscurely to have intimated, when he says; Let a man so account of us, as of the ministers of Christ, and the dispensers of the mysteries of God. And indeed it is sufficiently manifest that he himself exercised this power,- as in many other things, so in regard of this very sacrament; when, after having ordained certain things touching the use thereof, he says; The rest I will set in order when I come. Wherefore, holy Mother Church, knowing this her authority in the administration of the sacraments, although the use of both species has,--from the beginning of the Christian religion, not been unfrequent, yet, in progress of time, that custom having been already very widely changed,--she, induced by weighty and just reasons,- has approved of this custom of communicating under one species, and decreed that it was to be held as a law; which it is not lawful to reprobate, or to change at plea sure, without the authority of the Church itself.

Translation: J. Waterworth, The Canons and Decrees of the Council of Trent (1848), Hanover Historical Texts Project transcription (1995).