Among other arguments by defenders of the new calendar are those made on the basis of "truth" (notwithstanding that the detractors of that calendar make the claim that the Old Style date, , is the "true" celebration of Christ's Nativity). Arguments from truth can take two forms: (1) If a calendar is a system for reckoning time based on the motions of astronomical bodies—specifically the movements of Sun and Moon, in the case of the church calendar—and if precision or accuracy is understood as one aspect of truth, then a calendar that is more accurate and precise with respect to the motions of those bodies must be regarded as truer than one that is less precise. In this regard, some of those who champion the old calendar as "truth" (rather than for pastoral reasons, as seems to be the case with the national churches that adhere to it) may appear, to those following the new calendar, as the defenders of a fiction. (2) Some defenders of the new calendar argue that the celebration, in any way or form, of two feasts of Christ's Nativity within the same liturgical year is not possible, since according to the faith there is only one celebration of that feast in a given year. On this basis, they argue that those who prefer to observe a "secular" feast of the Nativity on and a "religious" one on , err in respect of the truth that there is but one feast of the Nativity each year.