The Doctrine of Double Effect

The doctrine of double effect holds that it can be permissible to bring about a harm as a foreseen but unintended side effect of pursuing a good end, even though it would be impermissible to bring about the same harm as a means or end.

Definition

The doctrine of double effect is the claim that an otherwise impermissible harm may be permissible when it is a merely foreseen side effect of an act aimed at a proportionate good, provided the good is not achieved by means of the harm and the harm is not intended.

Scope

This topic covers the doctrine of double effect: its conditions, its grounding in the moral significance of the intended/foreseen distinction, its application to cases such as the trolley problem and end-of-life care, and the principal objections to it. It treats double effect as a structural principle within deontology that constrains how harms may be brought about.

Core questions

• Is there a morally significant difference between intending a harm and merely foreseeing it?
• What conditions must be met for a harmful side effect to be permissible?
• Can double effect explain intuitions about cases like the trolley problem and terminal sedation?
• Does intention bear on the permissibility of an act, or only on the agent's character?

Key theories

The intended/foreseen distinction

The core claim that harms intended as ends or means are subject to stricter prohibition than equal harms that are merely foreseen and not intended, even when both are brought about knowingly.

Quinn's rights-based reconstruction

Quinn's account explaining double effect through the special objection a victim has to being deliberately used or involved in another's plans, rather than merely harmed as a side effect.

History

The doctrine originates with Aquinas's discussion of self-defence in the Summa Theologiae, where killing an assailant may be permissible as an unintended effect of self-preservation. Foot (1967) brought it into contemporary debate through the trolley and abortion cases, and Quinn (1989) reconstructed it in terms of the wrong of harmfully using a person, shaping ongoing discussion in ethics and bioethics.

Debates

The moral relevance of intention to permissibility

Critics such as Thomson argue that an agent's intention bears on the assessment of the agent, not on whether the act is permissible; defenders insist intention can make an objective moral difference.

The closeness problem

It is difficult to specify when a harm is 'intended as a means' rather than a side effect, since agents can redescribe their intentions to evade the doctrine.

Key figures

• Thomas Aquinas
• Philippa Foot
• Warren Quinn
• Frances Kamm

Seminal works

• aquinas1485
• foot1967
• quinn1989

Frequently asked questions

What are the conditions of the doctrine of double effect?

Standard formulations require that the act itself not be wrong, that the bad effect not be intended as an end or a means, that the good effect not be produced by means of the bad effect, and that there be a proportionate reason for permitting the bad effect.

Where is double effect applied?

It is invoked in just-war reasoning about civilian casualties, in bioethics regarding pain relief that may hasten death, and in trolley-style thought experiments distinguishing redirecting harm from using a person as a means.