By BRANDON L. WANLESS, PhD (cand.)
THE doctor communis of the Roman Church, St. Thomas Aquinas, is often neglected by contemporary liturgists and sacramental theologians because he is seen as unable to contribute to the liturgical reforms enacted after the Vatican Council II. In the context of the entire tradition, however, Aquinas is a pivotal contributor to the development of sacramental theology and practice. In the tertia pars of his Summa theologiae we find Aquinas’s most mature articulation of sacramental theology, in which he treats the sacraments of baptism, confirmation, eucharist, and penance individually. In particular, in what follows below, I examine how Aquinas provides the theological ratio underpinning the words of the sacramental formulae, namely, of baptizing, confirming, and absolving precisely “in the name of” the Trinity and not simply in or into “the Father, the Son, and the Holy Spirit.”
Regarding the sacrament of baptism, Aquinas notes that the form of the sacrament (i.e., the words used in administering the rite) determines its consecration as a holy action and therefore it also expresses the cause of the grace bestowed. “Now this cause is twofold; the principal cause from which it derives its virtue, and this is the Blessed Trinity; and the instrumental cause, viz. the minister who confers the sacrament outwardly.” Aquinas argues that both the instrumental cause and the ultimate efficient cause should be referenced in the form of the sacrament, since the form determines what the action is, namely a sacramental bestowal of grace. “Now the minister is designated by the words, 'I baptize thee'; and the principal cause in the words, 'in the name of the Father, and of the Son, and of the Holy Ghost.'” As opposed to the Eastern practice of passively declaring the sacramental action (“N. is baptized...”), Aquinas affirms and defends the Western practice of the minister himself (“Ego”) actively indicating the effect of the action “in the name of” the Trinity. Additionally, Aquinas echoes the tradition of the Church Fathers in his assertion that the singular “name” of the Trinity is used instead of several “names” to indicate that the effect derives from God's unified essence.
Aquinas’s treatment of confirmation is essentially the same as that of baptism. Regarding the sacrament of confirmation, he notes that “a sacramental form should contain whatever belongs to the species of the sacrament.” The species of the sacrament is what determines the essence of the sacrament; in the case of confirmation, he lists three necessary things which belong to the species: the cause, the effect, and the sign. “The first of these is the cause conferring the fulness of spiritual strength, which cause is the Blessed Trinity: and this is expressed in the words, 'In the name of the Father,' etc.” Responding to the objection that the Scriptures provide no evidence of this formula's institution, Aquinas replies that either the apostles passed on the formula in oral tradition or simply bestowed the effect of the sacrament without the later matter or form, the latter of which seems most historically plausible. Finally, because the sacrament is conferred only by the bishop, Aquinas finds it even less necessary, though still appropriate, to administer confirmation with the indicative formula using the first person, “Ego,” as the intention of such an exalted minister is less susceptible to corruption.
In addressing the form of penance, Aquinas describes the actions (words and deeds) of the penitent as the matter of the sacrament, while attributing the form to the words of absolution granted by the priest. Because sacraments “effect what they signify,” the significance of the form should correspond to “what the sacrament accomplishes” with respect to the matter; however, unlike baptism and confirmation, which consist in the application and use of material objects (water and oil), penance has no “use” of its matter, but rather “the removal of certain matter, namely sin.” Therefore, to remove the sins by the words, “I absolve you,” is most fitting. Regarding the rest of the Trinitarian formula, Aquinas asserts:
God alone on his own authority absolves from sin and pardons sins. The priests do both ministerially, that is, inasmuch as the words of the priest in this sacrament work instrumentally, just as in the other sacraments. … Yet, because the priest absolves as minister, it is only right that reference to the supreme authority of God be appended, as he says, “I absolve you in the name of the Father and of the Son and of the Holy Spirit.”
Finally, Aquinas here provides the clearest articulation of his teaching on the instrumentality of the sacramental minister: “God alone on his own authority absolves … the priests do so ministerially.” This same ratio is easily applied (“just as in the other sacraments”) to what is already implicit in his articles on baptism and confirmation: God alone on his own authority removes sin and grants the grace of adoption in baptism, and God alone perfects and strengthens the baptized in confirmation. Because the ministers act as instruments of God's power, they administer the sacraments ministerially, on behalf of, or “in the name” of the Blessed Trinity who alone effects the grace.
 Summa theologiae III, q. 66, a. 5. It is interesting to observe that, setting aside the divine command in Matthew 28:19, Aquinas does not regard the baptismal formula as “necessary” but only as “suitable.” Thus, this article is basically an argument of fittingness, for God easily could have chosen another means of this grace. Regarding the Trinity as principal agent vis-a-vis the triple immersion, cf. IIIa, q. 66, a. 8 ad 1: “Now the likeness of the agent enters into the effect, in regard to the form and not in regard to the matter. Wherefore the Trinity is signified in Baptism by the words of the form. Nor is it essential for the Trinity to be signified by the manner in which the matter is used; although this is done to make the signification clearer.”
 III, q. 66, a. 5.
 Aquinas acknowledges the practice of the “Greeks” as legitimate “in order to avoid the error of those who in the past ascribed the baptismal power to the baptizers.” St. Thomas observes, then, that the “Ego...” in the Western formula “is not essential; but it is added in order to lay greater stress on the intention.” Summa theologiae IIIa, q. 66, a. 5 ad 1.
 Cf. III, q. 66, a. 5 ad 6: “Although there are three personal names of the three Persons, there is but one essential name. Now the Divine power which works in Baptism, pertains to the Essence; and therefore we say, 'in the name,' and not, 'in the names.'”
 III, q. 72, a. 4.
 III, q. 72, a. 4.
 III, q. 72, a. 4 obj. 1, ad 1.
 III, q. 72, a. 4 ad 3.
 III, q. 84, a. 3.
 III, q. 84, a. 3 ad 3.