The Principle of
This principle aims to provide specific guidelines for determining
when it is morally permissible to perform an action in pursuit of a good
end in full knowledge that the action will also bring about bad results.
The principle has its historical roots in the medieval natural law
tradition, especially in the thought of Thomas Aquinas (1225?-1274),
and has been refined both in its general formulation and in its
application by generations of Catholic moral theologians. Although
there has been significant disagreement about the precise formulation of
this principle, it generally states that, in cases where a contemplated
action has both good effects and bad effects, the action is permissible
only if it is not wrong in itself and if it does not require that one
directly intend the evil result. It has many obvious applications to
morally complex cases in which one cannot achieve a particular desired
good result without also bringing about some clear evil. The principle
of double effect, once largely confined to discussions by Catholic moral
theologians, in recent years has figured prominently in the discussion
of both ethical theory and applied ethics by a broad range of
Formulation of the Principle. Classical formulations of the
principle of double effect require that four conditions be met if the
action in question is to be morally permissible: first, that the action
contemplated be in itself either morally good or morally indifferent;
second, that the bad result not be directly intended; third, that the
good result not be a direct causal result of the bad result; and
fourth, that the good result be "proportionate to" the bad result.
Supporters of the principle argue that, in situations of "double effect"
where all these conditions are met, the action under consideration is
morally permissible despite the bad result.
Each of these conditions has, however, been a matter of considerable
controversy. The first condition requires some criterion independent of
an evaluation of consequences for determining the moral character of the
proposed action. Moral philosophers who believe that the moral
character of an action is exhaustively determined by the nature of its
consequences will, of course, object to this requirement.
The second condition assumes that a sharp distinction can be drawn
between directly intending a result and merely foreseeing it. This
requirement has been the subject of much debate. Some philosophers argue
that if an agent recognizes that a certain consequence will inevitably
follow from a contemplated action, then in performing the action the
agent must be intending the consequence. Others argue, less strongly,
that defenders of double effect have failed to delineate a practicable
criterion for marking off the intended from the merely foreseen.
Defenders of the principle typically respond by pointing to the implicit
recognition of the moral significance of this distinction in the moral
practices of ordinary persons.
The third condition writes into the principle of double effect the
so-called Pauline principle, "One should never do evil so that good may
come." Again, philosophers who reject the view that actions can have a
moral character independent of their consequences will find this condition
The fourth condition, by bringing in the notion of proportionality,
has seemed to many philosophers to undercut the absolutism presupposed
by the first condition. Although the first three conditions have a
decidedly anticonsequentialist character, the fourth may appear to
embrace consequentialist reasoning. Defenders of the principle typically
attempt to accommodate the consequentialist character of the fourth
condition while ensuring that it does not render the more complex
features of the principle irrelevant.
Applications. The principle of double effect has played a
significant role in the discussion of many difficult normative
questions. Its most prominent applications are in medical ethics, where
it figures prominently in attempts to distinguish among permissible and
impermissible procedures in a range of obstetrical cases. The Catholic
magisterium has argued that the principle allows one to distinguish
morally among cases where a pregnancy may need to be ended in order to
preserve the life of the mother. The principle is alleged to allow the
removal of a life-threatening cancerous uterus, even though this
procedure will bring the death of a fetus, on the grounds that in this
case the death of the fetus is not "directly" intended. The principle
disallows cases, however, in which a craniotomy (the crushing of the
fetus's skull) is required to preserve a pregnant woman's life, on the
grounds that here a genuine evil, the death of the fetus, is "directly"
intended. There there is significant disagreement, even among those
philosophers who accept the principle, about the cogency of this
application. Some philosophers and theologians, by emphasizing the
fourth, "proportionality," condition, argue that the greater value
attaching to the pregnant woman's life makes even craniotomy morally
acceptable. Others fail to see a morally significant difference between
the merely "foreseen" death of the fetus in the cancerous uterus case
and the "directly" intended death in the craniotomy case.