Can a person be baptized against their will, according to Catholicism? In the 2006 film Nacho Libre, there is a scene where Ignacio, a Roman Catholic (but not an ordained priest), decides to sneak up on his tag partner Steven and baptize him, despite Steven not wanting anything to do with the church.

Ignacio: I'm a little concerned right now. About…your salvation and stuff. How come you've not been baptized?
Steven: Because I never got around to it, okay?
[Ignacio shrugs and starts to fill up a bowl with water]
Steven: I don't know why you always have to be judging me. Because I only believe in science.
[Ignacio finishes filing the bowl with water and starts walking up behind Steven]
Ignacio: But tonight, we are going up against Satan's cavemen. [Makes the sign of the cross] And I just thought it would be a good idea if you … [dunks Steven's head in the water] are baptized!
[Steven is in shock]
Ignacio: Felicidades.

While this is played for comedy, would forced baptism, like that shown in Nacho Libre, be valid according to Catholicism? What would be the rationale if it isn't?
In short, the answer is “no.”

Even for the Catholic Church, according to which Baptism is an instrument through which saving (sanctifying) grace is infused into a person’s soul, a forced baptism or baptism imposed by trickery would not be valid.

St. Thomas Aquinas, in his treatise on Baptism (part of the Summa theologiae) explains as follows:


  I answer that, By Baptism a man dies to the old life of sin, and begins a certain newness of life, according to Rm. 6:4: “We are buried together with” Christ “by Baptism into death; that, as Christ is risen from the dead … so we also may walk in newness of life.” Consequently, just as, according to Augustine [Serm. 351], he who has the use of free-will, must, in order to die to the old life, “will to repent of his former life”; so must he, of his own will, intend to lead a new life, the beginning of which is precisely the receiving of the sacrament. Therefore on the part of the one baptized, it is necessary for him to have the will or intention of receiving the sacrament (Summa theologiae, IIIa, q. 68, a. 7).


If the receiver of baptism, then, were opposed to receiving the sacrament, or (as in the case described in the O.P.) it were conferred on him without his consent, then it would be invalid.

(Of course, pretending to receive baptism while internally refusing to allow it to occur, or else—as in the O.P.’s example—forcing or tricking someone into being baptized, is at least objectively a grave sacrilege. Although I am not familiar with the story, it seems as though Ignacio is well-intentioned but misguided.)

Note that, at least as far as the Catholic Church is concerned, although a person with the use of reason (and hence the ability to make free-will decisions) can prevent Baptism from taking place by an internal act of the will, there is nothing to prevent infants from being baptized. Infants, not having the ability to make free-will decisions, cannot place an obstacle to baptism, and so it takes place in them without fail.

(I will also observe that Ignacio’s attempt at baptism would have been invalid, even if it were not against Steven’s will, because the Trinitarian formula is necessary for validity. See the Catechism of the Catholic Church 1239-1240.)

A note about Aquinas’ notion of intention

In discussing the sacraments, most Catholic theologians use Aquinas’ notion of intention, which would be good to recall. The term intention, which comes from the Latin in (which translates better in this case as “toward” or “into” than the English “in”) and tendere (to tend). Intention, then refers to any tendency toward an end.

In Aquinas, intention gets special attention when he speaks about our faculties and other natural tendencies. When applied to these, intention refers to the actuation of these faculties and tendencies in response to their proper object. For example, the proper object of the intellect is the beings that exist in the world around us, and so the concepts that we form about these beings can be called intentions.

However, intention can also apply to the will (which is the usage most familiar to us nowadays). In the case of the will, it specifically refers to choosing the means so as to obtain an end. I have the intention to go for a walk, as soon as I start to put on by walking shoes and go for the door (which are the means required for me to go for a walk).

That is the precise meaning that Aquinas gives when he says (in the passage I quoted above)


  so must he, of his own will, intend to lead a new life, the beginning of which is precisely the receiving of the sacrament.


and


  it is necessary for him to have the will or intention of receiving the sacrament


That means that you can’t just sneak up on a (conscious, adult) person and baptize him without his knowledge. The receiver’s will has to be involved and actually want the baptism (provided, of course, that it is not physically impeded: as is the case in infants, or in comatose or unconscious persons, or mentally handicapped persons).