Chapter — Prümmer, Manuale Theologiae Moralis
Chapter VI. On The Subject Of Baptism
124. Principle. The subject capable of baptism is every and only man who is a wayfarer and has not yet been baptized.147
It is said, first: every man who is a wayfarer. Therefore, no exception is given; and consequently, if anyone were miraculously born without original sin, he would still need baptism in order to receive the baptismal character and to be incorporated into the Church.148 Hence theologians commonly teach that even the Blessed Virgin Mary was baptized.149 That little children are capable of baptism even before the use of reason has been defined as of faith several times, for example, in the Council of Trent:150 "If anyone says that little children, because they have no act of believing, are not to be numbered among the faithful after receiving baptism, and therefore are to be rebaptized when they arrive at the years of discretion; or that it is better that their baptism be omitted than that, not believing by their own act, they be baptized in the faith of the Church alone, let him be anathema." The reason is that, just as in the Old Law infants were circumcised to destroy original sin, so a fortiori in the New Law infants are to be baptized to obtain the same effect. Moreover, without baptism eternal salvation is not given to one who dies, as was said above. Now, a great danger of death threatens little children especially. Therefore, they are to be baptized as soon as possible. When a man is no longer a wayfarer but is dead, he cannot be baptized, because all the sacraments were instituted for the living alone.
It is said, second: one who has not yet been baptized, because baptism cannot be repeated.
147 Code of Canon Law, c. 745.
148 Cf. St. Thomas, S. theol. 3, q. 68, a. 1 ad 3.
149 Benedict XIV, De canoniz. sanct., l. 4, P. 2, c. 21, n. 14.
125. Dispositions of the subject. In infants no disposition is required in order that they may be validly and licitly baptized. The same applies to adults who are perpetually insane, since they are equated with infants. But if insane persons enjoyed the use of reason before they fell into insanity, they cannot be validly baptized unless, before contracting insanity, they manifested in some manner the will to receive baptism. But if a doubt exists concerning such a manifestation, they can be baptized under condition, especially if they are in danger of death.151 When, after baptism thus conditionally conferred, an insane person unexpectedly recovers the use of reason, an investigation concerning his intention is to be made; and after that investigation has been made, if any doubt remains, baptism is to be repeated conditionally.
In adults, for the valid reception of baptism, at least a habitual intention is required, as is evident from what was said above, n. 87, concerning the sacraments in general, and will be said again below, n. 135.
After these things have been said concerning the subject who can be validly baptized, certain special precepts enacted by the Church are to be presented: 1. concerning the baptism of infants both of Catholics and of non-Catholics; 2. concerning the baptism of unborn or abortive fetuses; 3. concerning the baptism of adults.
151 Code of Canon Law, c. 754, § 3.