By Father Edward McNamara, LC
ROME, 28 January 2014 (ZENIT)
Answered by Legionary of Christ Father Edward McNamara, professor of liturgy and dean of theology at the Regina Apostolorum university.
Q: Should it happen that a diocesan bishop participates in a Mass in which he doesn't concelebrate, will he sit at his cathedra? What will be his proper vestments in this occasion? — W.B., Musoma, Tanzania
A: This question is foreseen in several documents, above all the Ceremonial of Bishops.
There are several occasions when the diocesan bishop could participate in Mass without concelebrating. For example, if a bishop attends a Mass celebrating a priest's jubilee anniversary, or a funeral for a priest's parent, he will often not concelebrate because the bishop would have the obligation to preside at the Mass.
This question was posed a few years ago to the Congregation for Divine Worship, which replied in its official review Notitiae (46  page 170). To wit:
"Whether it is permissible for a Bishop to concelebrate on the occasion of the jubilee of a certain priest such that he takes a place among the presbyters and yields the place of principal celebrant to the presbyter who is celebrating his jubilee?
"R. In the negative.
"The liturgical norm in force, which carries with it a theological principle rooted in the wisdom of the Fathers, confirms with all evidence the necessity that the Bishop preside at the celebration, whether he celebrates the Eucharist or not.
"The Ceremonial of Bishops in n. 18 says 'In every community of the altar gathered together under the Bishop as its sacred minister, the symbol of that charity and unity of the mystical Body, without which there can be no salvation, is shown. It is most fitting, therefore, that when the Bishop is present at a particular liturgical action, where the people is gathered, that he, as the one signed with the fullness of the sacrament of Order, presides at the celebration. This is not done to increase the exterior solemnity of the rite but to signify in a more vivid light the mystery of the Church. It is fitting also that the Bishop should join presbyters with himself in the celebration. If, however, the Bishop presides at the Eucharist but does not celebrate it, he himself takes charge of the liturgy of the word and concludes the Mass with the rite of dismissal.'
"Nevertheless, 'for a just cause he may be present at a Mass but not celebrate it, it is preferable, unless another Bishop is to celebrate, that he preside at the celebration, at least by celebrating the liturgy of the word and blessing the people at the end. This counts especially with regard to those eucharistic celebrations in which some sacramental rite or rite of consecration or blessing is to take place' (n. 175). In this case, the Bishop participates at Mass 'dressed in mozzetta and rochet, not in the cathedra but in a more suitable place prepared for him' (n. 186)."
I must say that the second part of this reply, fusing Nos. 175 and 186 of the Ceremonial of Bishops, is somewhat confusing, and, at least as refers to the vesture of the bishop seems to give incorrect information.
The Ceremonial of Bishops distinguishes two distinct situations. The first is when the bishop presides at the Liturgy of the Word and gives the final blessing but does not concelebrate. The proper vesture for this occasion is described in No. 176 of the CB. It is alb, pectoral cross, stole and cope of the color of the day, the miter and the pastoral staff. The CB, in Nos. 177-185, describes the ceremonial actions to be carried out on this occasion. In this situation the bishop will be seated at the cathedra (CB, 178).
The second situation, in which the bishop is present but does not preside, is described in CB No. 186. On these occasions the bishop wears what is known as choir dress.
This consists of the fuschia- or purple-colored cassock along with mozzetta and zucchetto or skullcap of the same color. The mozzetta is a small, hooded cape extending to the elbows and buttoned in front.
The biretta, a square, stiff brimless cap with three or four ridges on the top surface and worn over the skullcap, is no longer obligatory and is now rarely used.
The rochet is worn under the mozzetta and over the cassock. It is a white linen vestment resembling a surplice except that it has close fitting sleeves rather than the wide ones of the surplice.
Over the mozzetta he wears a pectoral cross which is usually hung on a gold and green cord, although some bishops use a silver- or gold-colored chain for all occasions.
In this case the bishop is not seated at the cathedra but at some other suitable place within the presbytery.
On some occasions there may be a combination of both modes of vesture, for example, if the bishop is in choir dress but is to make the final commendation at a funeral. In this case, after communion he removes the mozzetta and replaces it with the cope, stole and miter in order to direct the prayers.