I don't understand the quote form Fr. Hunter. A change in the essential form would not be going through "the outward act required by the rite" according to the position of Catharinus. That a minister can change the essential form is irrelevant, Catharinus' po
sition is that the required form and matter is observed. If I am observing someone baptize another, and I can clearly hear the words pronounced as they should be and the water is poured as it should be, then I have absolute certainly the sacrament of baptism was performed. A pagan can scoff at their friends wish of being baptized, but if his friend requests baptism from him, and he perform the baptism as he should, and the pagan scoffs at his friend's Catholic belief, regardless the baptism is absolutely valid.
To follow through with the required form and matter is in itself an intention to do as the Church does. One does not say in his heart, "I will not baptize my friend", and then proceed to baptize his friend. That the pagan wills that the words of baptism proceed out of his mouth, and his hand pour the water over his friend's head, is to intend to do what the Church does.
To say in your heart, "I will not baptize my friend", is irrelevant.
Who uttered the words, "I baptize thee. . ."? The pagan.
Who poured the water? The pagan.
What are the odds a neurological disorder could result in the words of baptism being pronounced, and at the same time, his hand pour the water without his intending to do so? It's impossible.
Whence came the command to speak and to pour the water? The pagan's own soul commanded his body that he should act thus.
Sean's quote is from Outlines of Dogmatic Theology, Volume III,
pages 210 to 211
Fr. Hunter continues (refuting Ladislaus):
[. . .]
“In the view of Catharinus, no other intention is required in the minister of a Sacrament than that he should deliberately go through the outward acts required by the rite ; and this is held to be sufficient, though the minister have no interior intention of doing what the Church does, and even if he interiorly form an explicit act of not intending so to do. But this theory fails to secure the absolute certainty that the Sacrament is valid, for it is easy for the minister to change the words of the form (n. 680) in an essential particular without this fraud being detected."
Hunter then quotes the condemnation by Alexander VIII in support of all the above.