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BASTA 2017

At the Bay Area St Thomas Aquinas Association (BASTA) dinner in 2017, Professor Thomas Cavanaugh of the Philosophy Department of the University of San Francisco delivered a talk entitled “Duplex Effectus and Double Effect.” He began by discussing the locus classicus of double effect, Aquinas’s consideration of a private individual’s act of self-defense (Summa theologiae, IIaIIa, q. 64, a. 7). Professor Cavanaugh noted that Aquinas pithily says, “nothing prevents one act from having double (or, two) effects (in the Latin, duplex effectus), one of which is intended, the other of which is beside intention (Summa theologiae, IIaIIae q. 64, a. 7, body of the article).” Professor Cavanaugh went on to note that this observation and the criteria Aquinas employs in evaluating the justice of the contemplated act come to be called what Cavanaugh refers to as ‘double-effect reasoning’. Professor Cavanaugh discussed reasons for preferring this name to the more common ‘principle’, ‘rule’, or ‘doctrine’ of double effect’.

Professor Cavanaugh noted that in Aquinas’ discussion of double effect, the angelic doctor addresses otherwise wholesome acts in which an agent pursues a good inextricably bound up with a bad effect. Such acts implicate the first precept of the natural law; namely, that we ought to do and pursue the good while avoiding the bad (Summa theologiae, IaIIae, q 94, a. 2). As Professor Cavanaugh noted, this raises a salient question: must an agent forego pursuit of the good when the act productive of the good will also effect the bad? Professor Cavanaugh proposed that this is the question Aquinas answers by means of double-effect reasoning in his discussion of a private individual’s act of self-defense that also results in the death of the aggressor.

Moving forward, Professor Cavanaugh noted that the context within which Aquinas contemplates a private individual’s self-defense that results in the death of the assailant importantly differs from our current circumstances. For example, as Professor Cavanaugh noted, many contemporary jurisdictions grant a private individual the authority intentionally to kill in self-defense – a possibility Aquinas appears to regard as in principle licit, but which he does not explicitly address. Rather, as Cavanaugh noted, Aquinas considers the (presumably, default) case in which a jurisdiction has not so extended authority to private individuals intentionally to kill in self-defense. Putting such specifics to the side, Cavanaugh went on to propose that one discerns in Aquinas’s inchoate account of double effect the following set of criteria for evaluating acts in which the good we ought to pursue cannot be extricated from the bad we ought to avoid, or cases of double effect:

1) the act considered independently of its bad effect is not in itself wrong;

2) the agent intends the good and does not intend the bad either as an end or as a means; and,

3) the agent has proportionately grave reasons for acting, addressing his relevant obligations, comparing the consequences, and, considering the necessity of the bad, exercising due care to eliminate or mitigate it.

Professor Cavanaugh argued on behalf of each of these criteria. In particular, he argued for the ethical relevance of distinguishing intended effects from foreseen but not intended effects in act-evaluation. He concluded the talk by considering a contemporary application of double effect, often referred to as palliative sedation at the end of life. Relying on double effect, he contrasted such an act with both and voluntary active euthanasia. He proposed that in an act of terminal sedation one need not intend the death of the patient while in PAS or euthanasia, one necessarily would. A lively discussion followed.


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