Summa Theologica, by St. Thomas Aquinas, [1947], at sacred-texts.com
We must now consider those who confer this sacrament. Under this head there are two points of inquiry:
(1) Whether a bishop alone can confer this sacrament?
(2) Whether a heretic or any other person cut off from the Church can confer this sacrament?
Objection 1: It would seem that not only a bishop confers the sacrament of Order. For the imposition of hands has something to do with the consecration. Now not only the bishop but also the assisting priests lay hands on the priests who are being ordained. Therefore not only a bishop confers the sacrament of Order.
Objection 2: Further, a man receives the power of Order, when that which pertains to the act of his Order is handed to him. Now the cruet with water, bowl* and towel, are given to the subdeacon by the archdeacon; as also the candlestick with candle, and the empty cruet to the acolyte. [*"Bacili." The rubric has "aquamanili." Some texts of the Summa have "mantili" ("maniple"), but the archdeacon does not give the maniple to the subdeacon.] Therefore not only the bishop confers the sacrament of Order.
Objection 3: Further, that which belongs to an Order cannot be entrusted to one who has not the Order. Now the conferring of minor Orders is entrusted to certain persons who are not bishops, for instance to Cardinal priests. Therefore the conferring of Orders does not belong to the episcopal Order.
Objection 4: Further, whoever is entrusted with the principal is entrusted with the accessory also. Now the sacrament of Order is directed to the Eucharist, as accessory to principal. Since then a priest consecrates the Eucharist, he can also confer Orders.
Objection 5: Further, there is a greater distinction between a priest and a deacon than between bishop and bishop. But a bishop can consecrate a bishop. Therefore a priest can ordain a deacon.
On the contrary, Ministers are applied by their Orders to the Divine worship in a more noble way than the sacred vessels. But the consecration of the vessels belongs to a bishop only. Much more therefore does the consecration of ministers.
Further, the sacrament of Order ranks higher than the sacrament of Confirmation. Now a bishop alone confirms. Much more therefore does a bishop alone confer the sacrament of Order.
Further, virgins are not placed in a degree of spiritual power by their consecration, as the ordained are. Yet a bishop alone can consecrate a virgin. Therefore much more can he alone ordain.
I answer that, The episcopal power stands in the same relation to the power of the lower Orders, as political science, which seeks the common good, to the lower acts and virtues which seek some special good, as appears from what was said above (Q[37], A[1]). Now political science, as stated in Ethic. i, 2, lays down the law to lower sciences, namely what science each one ought to cultivate, and how far he should pursue it and in what way. Wherefore it belongs to a bishop to assign others to places in all the Divine services. Hence he alone confirms, because those who are confirmed receive the office, as it were, of confessing the faith; again he alone blesses virgins who are images of the Church, Christ's spouse, the care of which is entrusted chiefly to him; and he it is who consecrates the candidates for ordination to the ministry of Orders, and, by his consecration, appoints the vessels that they are to use; even as secular offices in various cities are allotted by him who holds the highest power, for instance by the king.
Reply to Objection 1: As stated above (Q[37], A[5]), at the imposition of hands there is given, not the character of the priestly Order, but grace which makes a man fit to exercise his Order. And since those who are raised to the priesthood need most copious grace, the priests together with the bishop lay hands on them, but the bishop alone lays hands on deacons.
Reply to Objection 2: Since the archdeacon is as it were minister-in-chief, all things pertaining to the ministry are handed by him, for instance the candle with which the acolyte serves the deacon by carrying it before him at the Gospel, and the cruet with which he serves the subdeacon; and in like manner he gives the subdeacon the things with which the latter serves the higher Orders. And yet the principal act of the subdeacon does not consist in these things, but in his co-operation as regards the matter of the sacrament; wherefore he receives the character through the chalice being handed to him by the bishop. On the other hand, the acolyte receives the character by virtue of the words of the bishop when the aforesaid things---the cruet rather than the candlestick---are handed to him by the archdeacon. Hence it does not follow that the archdeacon ordains.
Reply to Objection 3: The Pope, who has the fulness of episcopal power, can entrust one who is not a bishop with things pertaining to the episcopal dignity, provided they bear no immediate relation to the true body of Christ. Hence by virtue of his commission a simple priest can confer the minor Orders and confirm; but not one who is not a priest. Nor can a priest confer the higher Orders which bear an immediate relation to Christ's body, over the consecration of which the Pope's power is no greater than that of a simple priest.
Reply to Objection 4: Although the Eucharist is in itself the greatest of the sacraments, it does not place a man in an office as does the sacrament of Order. Hence the comparison fails.
Reply to Objection 5: In order to bestow what one has on another, it is necessary not only to be near him but also to have fulness of power. And since a priest has not fulness of power in the hierarchical offices, as a bishop has, it does not follow that he can raise others to the diaconate, although the latter Order is near to his.
Objection 1: It would seem that heretics and those who are cut off from the Church cannot confer Orders. For to confer Orders is a greater thing than to loose or bind anyone. But a heretic cannot loose or bind. Neither therefore can he ordain.
Objection 2: Further, a priest that is separated from the Church can consecrate, because the character whence he derives this power remains in him indelibly. But a bishop receives no character when he is raised to the episcopate. Therefore he does not necessarily retain the episcopal power after his separation from the Church.
Objection 3: Further, in no community can one who is expelled therefrom dispose of the offices of the community. Now Orders are offices of the Church. Therefore one who is outside the Church cannot confer Orders.
Objection 4: Further, the sacraments derive their efficacy from Christ's passion. Now a heretic is not united to Christ's passion; neither by his own faith, since he is an unbeliever, nor by the faith of the Church, since he is severed from the Church. Therefore he cannot confer the sacrament of Orders.
Objection 5: Further, a blessing is necessary in the conferring of Orders. But a heretic cannot bless; in fact his blessing is turned into a curse, as appears from the authorities quoted in the text (Sent. iv, D, 25). Therefore he cannot ordain.
On the contrary, When a bishop who has fallen into heresy is reconciled he is not reconsecrated. Therefore he did not lose the power which he had of conferring Orders.
Further, the power to ordain is greater than the power of Orders. But the power of Orders is not forfeited on account of heresy and the like. Neither therefore is the power to ordain.
Further, as the one who baptizes exercises a merely outward ministry, so does one who ordains, while God works inwardly. But one who is cut off from the Church by no means loses the power to baptize. Neither therefore does he lose the power to ordain.
I answer that, on this question four opinions are mentioned in the text (Sent. iv, D, 25). For some said that heretics, so long as they are tolerated by the Church, retain the power to ordain, but not after they have been cut off from the Church; as neither do those who have been degraded and the like. This is the first opinion. Yet this is impossible, because, happen what may, no power that is given with a consecration can be taken away so long as the thing itself remains, any more than the consecration itself can be annulled, for even an altar or chrism once consecrated remains consecrated for ever. Wherefore, since the episcopal power is conferred by consecration, it must needs endure for ever, however much a man may sin or be cut off from the Church. For this reason others said that those who are cut off from the Church after having episcopal power in the Church, retain the power to ordain and raise others, but that those who are raised by them have not this power. This is the fourth opinion. But this again is impossible, for if those who were ordained in the Church retain the power they received, it is clear that by exercising their power they consecrate validly, and therefore they validly confer whatever power is given with that consecration, and thus those who receive ordination or promotion from them have the same power as they. Wherefore others said that even those who are cut off from the Church can confer Orders and the other sacraments, provided they observe the due form and intention, both as to the first effect, which is the conferring of the sacrament, and as to the ultimate effect which is the conferring of grace. This is the second opinion. But this again is inadmissible, since by the very fact that a person communicates in the sacraments with a heretic who is cut off from the Church, he sins, and thus approaches the sacrament insincerely and cannot obtain grace, except perhaps in Baptism in a case of necessity. Hence others say that they confer the sacraments validly, but do not confer grace with them, not that the sacraments are lacking in efficacy, but on account of the sins of those who receive the sacraments from such persons despite the prohibition of the Church. This is the third and the true opinion.
Reply to Objection 1: The effect of absolution is nothing else but the forgiveness of sins which results from grace, and consequently a heretic cannot absolve, as neither can he confer grace in the sacraments. Moreover in order to give absolution it is necessary to have jurisdiction, which one who is cut off from the Church has not.
Reply to Objection 2: When a man is raised to the episcopate he receives a power which he retains for ever. This, however, cannot be called a character, because a man is not thereby placed in direct relation to God, but to Christ's mystical body. Nevertheless it remains indelibly even as the character, because it is given by consecration.
Reply to Objection 3: Those who are ordained by heretics, although they receive an Order, do not receive the exercise thereof, so as to minister lawfully in their Orders, for the very reason indicated in the Objection.
Reply to Objection 4: They are united to the passion of Christ by the faith of the Church, for although in themselves they are severed from it, they are united to it as regards the form of the Church which they observe.
Reply to Objection 5: This refers to the ultimate effect of the sacraments, as the third opinion maintains.