Late as I am I want to comment on the recent document from the PCED on the interpretation of the Motu Proprio Summorum Pontificum.
First, here is a summary of the main body of the document. You can see a scan of the letter, in Italian, on the NLM (where the translation also come from).
1. If there is no other possibility, because for instance in all churches of a diocese the liturgies of the Sacred Triduum are already being celebrated in the Ordinary Form, the liturgies of the Sacred Triduum may, in the same church in which they are already celebrated in the Ordinary Form, be additionally celebrated in the Extraordinary Form, if the local ordinary allows.
2. A Mass in the usus antiquior may replace a regularly scheduled Mass in the Ordinary Form. The question contextualizes that in many churches Sunday Masses are more or less scheduled continually, leaving free only very incovenient mid afternoon slots, but this is merely context, the question posed being general. The answer leaves the matter to the prudent judgement of the parish priest, and emphasises the right of a stable group to assist at Mass in the Extraordinary Form.
3. A parish priest may schedule a public Mass in the Extraordinary Form on his own accord (i.e. without the request of a group of faithful) for the benefit of the faithful including those unfamiliar with the usus antiquior. The response of the Commission here is identical to no. 2.
4. The calendar, readings or prefaces of the 1970 Missale Romanum may not be substituted for those of the 1962 Missale Romanum in Masses in the Extraordinary Form.
5. While the liturgical readings (Epistle and Gospel) themselves have to be read by
the priest (or deacon/subdeacon) as foreseen by the rubrics, a translation to the vernacular may afterwards be read also by a layman.
It is fair to say that all these points were already in the Motu Proprio, but (since clarification was requested), they needed reiterating. In particular, it is quite astonishing that point 3 needed making, but Twitter was filled with re-tweets on this point as if it were surprising. But Article 2 of the MP says that any priest may say a private Mass (Missa sine populo) without requiring any permission to do so, and article 4 clarifies that despite its confusing Latin name ('sine populo') people can actually attend these Masses. Furthermore, article 5 notes that scheduling public Masses requires only the permission of the priest in charge of the church or chapel. In other words, the two forms of the Roman Rite are exactly the same where permission to celebrate is concerned. (The same goes for the need for the priest to be 'idoneus' and not juridicially impeded.)
Point 2 is implicit in the Motu Proprio, though not explicit. Since the two Forms of the Rite are equally in the power of the Rector of a church or chapel, he may introduce one at a time formerly occupied by the other. If you think about it, you have to ask: why shouldn't he be able to do this?
Point 5 is the most interesting. It was a custom in certain places before the new Missal was introduced for a vernacular translation to be read by a layman after the priest had read or sung it in Latin. In some cases this was done simultaneously with the priest's reading in Latin. The ruling here makes allowance for this, on the condition that the Latin text be read by the priest first. It must be read, and it must be read first before anything else happens.
A great deal of confusion has arisen over the Motu Proprio Article 6, which says
In Missis iuxta Missale B. Ioannis XXIII celebratis cum populo, Lectiones proclamari possunt etiam lingua vernacula, utendo editionibus ab Apostolica Sede recognitis.
This led to some suggestions that it would be possible to use the lectionary of the 1970 Missal (which would lead to the use of the 1970 calendar as well); this is not supported by the text, however, and is now definitively ruled out by point 4 of the PCED's letter.
Another interpretation of the MP Article 6 was that the readings may read in the vernacular without them being read in Latin first. But that is not what the Latin says: Lectiones proclamari possunt etiam lingua vernacula means that it is possible to read them ALSO in the vernacular.
Unfortunately even the translation improved by Rorate Caeli and posted on their website fails to translate the 'etiam', as does the semi-official English translation provided by the Vatican Information Service on the Vatican website.
It is just possible that 'etiam' could mean 'even' (as in: 'on occasion'), but this is now ruled out by the PCED. The permission to have the translation read does not allow the Latin not to be read by the priest. The Latin texts of the epistle and gospel are part of the Mass.
That this should be so requires some explanation, which I propose to address in the next post.