Is Sunday considered a feast day or are you merely extrapolating the law? According to the calculation of time, both canonically and liturgically, the day begins at midnight. Attending Mass on Saturday is a de facto transfer of the Holy Day, yet there is no provision in law stating that this has occurred.
The Society confirms the canon in question applies to Sunday and that the Church has the right to make Masses on Saturday evening count for Sunday.
I don't dispute that the Church has the authority to change the day, that is the common opinion of theologians; what I dispute, and I'm sure Fr. Scott, among others would agree, is that the immediate context of the canon in question pertains to Feast Days and not every single Sunday of the year. Aside from the absurdity of having a "vigil" Mass for every Sunday, even if I granted that the law could be applied in the case of Sunday, you would still have to surmount the problem of interpreting the law as an exception and not the rule. Indeed, considering there has been no formal change of days (you have not cited the decree) the interpretation of the canon in question should be dictated by traditional jurisprudence.
In this case, the true sense of the canon would envisage a justifying excuse to attend Mass on Saturday to fulfill the obligation of Sunday,
an entirely different day. Consequently to understand the law as if it applied equally without distinction, without any need of a justifying cause, to Saturday as well as Sunday and thus a matter of mere preference, is erroneous. For that would imply a
de facto change from Sunday to Saturday (
per the calculation of time) and the law nowhere indicates that this is the
intention of the lawgiver. Thus the only rational interpretation of the canon is that it applies to those who have a justifying excuse to miss Mass on Sunday, but can attend on Saturday. The extension of which is an attempt at being equitable no doubt, but nevertheless,
an exception to the rule always requires a justifying cause.
The fact that it is a badly worded canon would certainly excuse many from mortal sin. But in the case of Bishops and priests, they are undoubtedly committing sin by leading people astray in this matter. For as a matter of fact, every single Catholic now believes that going to Mass on Saturday fulfills ones obligation equally well as attending on Sunday. This is certainly erroneous. Until such a time when the Church formally changes the day, it must be considered erroneous.