As I have noted before, Fr. Brian Harrison, O.S. has written on the question of torture in two parts: Part 1 and Part 2.

Fr. Harrison surveys various authorities, including St. Thomas Aquinas:

A7. St. Thomas Aquinas (13th century). The Angelic Doctor never treats of torture in secular judicial inquiries. However, without mentioning the word, he does justify the contemporary Inquisition’s use of torture (recently introduced in 1252 by Pope Innocent IV – cf. B4 below). Like Augustine eight centuries earlier justifying imperial force used against the Donatist schismatics, Thomas appeals in his sed contra to the Gospel itself: the compelle intrare of Lk 14: 23 (parable of the king and wedding guests). In considering whether unbelievers may be "compelled" to the faith, he first acknowledges that those who have never been Christians (i.e., Jews, pagans and Muslims) may not be forced to embrace the faith, but then continues: "On the other hand, there are unbelievers who at some time have accepted the faith, and professed it, such as heretics and all apostates: such should be submitted even to bodily compulsion, that they may fulfil what they have promised, and hold what they, at one time, received".22

Consistently with the fundamental idea of forcing a man to confess an offence, St. Thomas does not recognize for the accused a right corresponding to the U.S. Constitution’s Fifth Amendment. In considering whether one may lie to a judge in order to protect oneself, Aquinas teaches that while the accused is not bound to answer every possible question that might incriminate him, he may never lie, and indeed, is bound to answer the judge truthfully, revealing his own guilt, "under the laws of evidence" (secundum ordinem juris), as for instance when there are well-founded rumors, or clear indications, or semi-complete proof [of his guilt]".23

A8. St. Thomas Aquinas (13th century). He also discusses bodily mutilation (ST, IIa IIae 65, 1) and the thrashing of children by parents and slaves by their masters (65, 2). His justification of these practices as punishments for proven offences essentially just throws the ball back into a couple of other courts: (a) as regards authority, into that of Sacred Scripture, with the sed contra appealing in the case of mutilation to the lex talionis (Ex. 21: 24, Lv 24: 19-20), and to the books of Proverbs and Sirach in the case of flogging (cf. references A10-A15 in Part I of this study); and (b) as regards inherent reasoning, into that of capital punishment, using a simple a fortiori argument (i.e., if competent authority may legitimately take life itself as punishment, then all the more may it inflict lesser bodily penalties).

It is notable that St. Thomas himself does not expicitly hold that the use of torture to get a confession (or other information) is licit. At most, he maintains that those who once had the virtue of faith may be compelled through the use of force. But this seems inconsistent with the position that the virtue of faith is given through grace, and cannot be elicited by human effort alone. Is pain likely to move someone to open himself up to the movement of the Holy Spirit and away from his own beliefs? (How is it possible for a human judge to distinguish between a true apostate and heretic from someone who sincerely, or in accordance with his conscience, changes his mind about divine matters?)

Some may hold that torture is wrong because it offends against charity. But their argument, like the argument against capital punishment, fails because it does not distinguish punishment or 'rightful harm' from injury or wrongful harm. It needs to be shown that torture is wrong because it is against justice and is a form of injury. I think this can be done if we remember the definition of justice. Unless it is a form of retribution, the deliberate inflicting of some harm upon another is unjust and wrong.

Can someone be punished for disobedience? Or failing to comply with an order to give information when it has been determined by a competent authority that this information is vital to the common good, and that the subject possesses this knowledge? I think the answer to both questions is yes. But punishment for disobedience is not the same as inflicting pain or bodily harm in order to elicit information. The ratio of the moral act is different in each case, even though the object of the external act--producing pain or bodiliy harm, is the same.

I note that Fr. Harrison would seem to agree with the above assessment (see his conclusion for part 2). But he thinks that the question of whether torture may be used to extract information has not been answered by the Magisterium:

Thirdly, there remains the question – nowadays a very practical and much-discussed one – of torture inflicted not for any of the above purposes, but for extracting life-saving information from, say, a captured terrorist known to be participating in an attack that may take thousands of lives (the now-famous ‘ticking bomb’ scenario). As we have noted above, this possible use of torture is not mentioned in the Catechism. If, as I have argued, the infliction of severe pain is not intrinsically evil, its use in that type of scenario would not seem to be excluded by the arguments and authorities we have considered so far. (John Paul II’s statement about the "intrinsic evil" of a list of ugly things including torture in VS #80 does not seem to me decisive, even at the level of authentic, non-infallible, magisterium, for the reasons I have already given in commenting above on that text.) My understanding would be that, given the present status questionis, the moral legitimacy of torture under the aforesaid desperate circumstances, while certainly not affirmed by the magisterium, remains open at present to legitimate discussion by Catholic theologians.

Here is what I believe to be the problem -- the "infliction of severe pain" is not intrinsically evil if it has the character of punishment, in which case it is just. If it does not have the character of punishment, then it is always unjust. I cannot see how it could be otherwise. Hence, we are not dealing with a 'morally neutral' external act, but one which has already been determined to be unjust and therefore immoral. Using it for the sake of getting information would therefore be an instance of using an evil means in order to procure a perceived good end.

I think because of our relative ease in grasping justice, even if we cannot explain what justice is precisely, we have an natural or instinctive aversion to torture, which is worn away once we begin to accept consequentialism.