I’m told that Advent starts on Vespers the night before the first Sunday of Advent. Is this so? How about Can. 202 §1 ? In law, a day is understood to be a space of twenty-four hours, to be reckoned continuously and, unless expressly provided otherwise, it begins at midnight…
That canon contains the words "unless expressly provided otherwise". This is just such an occasion. Generally Vespers/Evening Prayer on Saturday is Evening Prayer I of Sunday and Evening Prayer on Sunday is Evening Prayer II of Sunday.
Note that the same applies to all Solemnities.
Advent is a liturgical season, not a canonical one. Hence it follows liturgical rules as to its start.
Canon law only uses the word “Advent” twice, and only one of those has canonical consequence: in the introduction, John Paul states that the code enters into force on the first day of Advent, 1983. Of course, that’s the start of a whole new liturgical calendar, but when he wrote it in early 1983, he was referring to the same canonical year. And for similar reasons, I suspect that the new code took effect at 12 midnight, the beginning of the canonical day Sunday, rather than Saturday evening.
[quote=Phemie]That canon contains the words “unless expressly provided otherwise”. This is just such an occasion. Generally Vespers/Evening Prayer on Saturday is Evening Prayer I of Sunday and Evening Prayer on Sunday is Evening Prayer II of Sunday.
I disagree with this interpretation, and one piece of evidence that supports my view is Canon 1248, which says one may fulfill his mass obligation on a feast day or the evening of the preceding day. There would be no need for this wording if canon law followed the liturgical day, and in fact it would be confusing.