Moral absolutes, and the role of the so-called principle of double effect, play an essential role in the discourse of those who are committed to natural law reasoning about contemporary moral issues. To give just one example, consider the on-going controversy about the placentectomy that was performed on an expectant mother in Phoenix who was suffering from pulmonary arterial hypertension, an operation that saved her life, but resulted in the death of her child. That controversy is precisely over whether the moral absolute against murder was violated, or whether the death of the child was a “side effect” and not an intentional abortion at all. Yet moral absolutes—what they are, why they obtain, and how they are to be applied—are not always well understood. Both with a view to casting light back over other essays I have written, and with a view to an upcoming essay on the intentional killing of innocent persons in war, I here offer some thoughts on the nature of this essential part of practical ethics.

The natural law view that underlies much of what I have written for Public Discourse is rooted in the idea of St. Thomas Aquinas that the principles of the natural law are directives toward human goods that are aspects of human well-being. Moving beyond St. Thomas, we could say that each basic good gives to human agents a basic reason for action, rooted in those aspects of human well-being and perfection promised by instances of those goods. But there are many such goods: human life and health, knowledge, aesthetic experience, work and play, friendship, marriage, personal integrity, and the good of religion.

Faced with a plurality of goods, the moral question is this: what should one do when one is faced with competing options in the pursuit of goods, options that are not all mutually pursuable? The suggestion that I make here is that one should be always and entirely open to all the goods, in all persons, and never act directly or intentionally against any of the goods in any persons. “Openness” here should be understood to encompass the demand of the goods that they be promoted and protected: one is not open to basic aspects of human well-being if one always does nothing. The goods call, in various ways, for action on their behalf. But in all such action, the core negative requirement of morality is that one never intentionally act so as to damage or destroy an instance of a basic good.

To repeat, basic goods are aspects of human well-being, and nothing but such aspects. In themselves, as I have argued in my discussion of capital punishment, they give us always a reason to promote and protect, and always a reason not to damage. So an ethic of human goods, an ethic that takes human well-being as a touchstone notion, must establish some very strong protections of goods to be respected in human action, for damage to human goods is damage to human well-being or flourishing. An ethic that was concerned with human flourishing but paid no attention to whether an act was damaging or destructive of human goods would make little sense.

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Yet it is impossible to go through life in service of human goods and human well-being without having some kind of negative impact upon basic human goods: even the choice to do this, rather than that, means that some goods will go unserved. In some cases, even fulfilling my obligations will have as a consequence some damage to basic goods: I thrust myself between my child and the attacker’s knife, for example, in order to save my child’s life; but I suffer grave damage to my own life in consequence. So a goods-based ethic rooted in human well-being cannot demand that whatever one does, one never in any way do anything that will bring harm upon instances of human goods. Such an ethic would be unworkable.

But one can always refrain from acting; and in this way, if in no other, one can always refrain from intentionally damaging instances of basic human goods. So we should conclude that the core constraint of ethics should and could be framed as a demand that one never intentionally damage or destroy an instance of a basic human good. This conclusion would only be strengthened were one to recognize that in many cases of positive action for the sake of some good, as in the case of my saving my child’s life, the unavoidable damage to the good—my life—is not intended. Rather, the harm I suffer is accepted as a side effect, but it is neither chosen as a means, nor willed as an end; in short, it is not intended.

This line of thought leads not only to the formulation of moral absolutes, but also to the so-called principle of double effect. With regard to absolutes, each will be framed as a negative requirement never to choose a particular kind of act that is always damaging to a basic good. So, a moral absolute regarding human life would be: never intentionally kill an innocent human being. (In fact, I believe that no human being should be intentionally killed, but we can put that aside for now.)

However, recognizing that some acts that have as a consequence the death of a human being are such that the death is not intended, the principle of double effect teaches that under certain circumstances—if the agent has not been negligent and has no other way to address the problem, and if the goods at stake are great and gravely threatened—then the agent may do something (save my child’s life) that is morally good, even though that action has as a side effect a consequence (harm to my life) that it would be wrong to intend. Particularly where the good of human life is concerned, the principle of double effect has been thought central to the defense of moral absolutes; for example, without it—if we had only a blanket prohibition against doing anything that harmed innocent life—it would be impossible to refuse a medical treatment, no matter how onerous or costly, if the refusal would shorten the patient’s life.

What emerges from the discussion concerning moral absolutes, then, is this: First, moral absolutes are essential to the protection of human goods, and hence human well-being. They are not “mere” restrictions or commands, with no relevance to the goods that matter to us.

Second, moral absolutes are to be understood as restricting certain kinds of intentional acts: intentional killing, for example. This leads, third, to the following important point: as so understood, moral absolutes are to be framed only by identifying a kind of act that, if it were chosen, would be such always as to involve the agent’s intending damage or destruction to a basic human good. Put another way, the acts picked out by moral absolutes do not themselves include a reference to their moral status; but they are such that they—acts of this kind—may be identified as always and everywhere wrong because of their negative relationship to human goods.

Descriptions of the moral absolute against murder thus go wrong if they identify the act that is prohibited as “unjust killing” or “killing one with a right to life.” Much better is: no intentional killing of innocent human beings. We may designate this kind of action by the name “murder.” And if, as I think, such acts as murder, so understood, are always directed against someone’s pursuit or enjoyment of basic goods, then one can conclude that the intentional killing of an innocent human being (murder) is always and everywhere wrong. Murder is thus not defined as wrongful killing (for then “murder is wrong” would be a mere tautology, trivially true). But, because all murder involves an intentional damaging of an instance of the basic good of human life, it is true that murder is always wrong.

There is, fourth and finally, an implication of the “absoluteness” of moral absolutes, an implication identified by every major figure of the Thomistic natural law tradition up until quite recently: absolutes are never to be violated, regardless of the consequences. This claim might seem almost comically obvious, were it not so routinely questioned, even by very serious proponents of the natural law, and even by members of faith traditions, such as the Catholic Church, who have accepted and promulgated the doctrine that there are moral absolutes. For routinely we find that even such persons of good will are doubtful that moral absolutes should be upheld in situations where many lives are at stake, or where horrible evils are threatened, or in situations, as they have come to be called, of “supreme emergency,” such as the Nazi threat against Europe, the Soviet threat against the free West, or the Islamist threat of al Qaeda.

As John Finnis and others have argued, even a conditional willingness to accept that moral absolutes may be put aside in such cases denudes the doctrine of moral absolutes of all its distinctive content: apparently, if such exceptions are to be contemplated, there will be situations in which the goods protected by the moral absolutes are outweighed or overridden by some conceivable set of harms or other achievable goods. But if such a possibility is available in principle, then not only are there no moral absolutes, there is also no reason to think that the boundary at which we meet restrictions against such actions as intentional killing of the innocent, false assertion, blasphemy, or adultery is far out, distant from our day-to-day considerations. Perhaps there are legitimate goods to be achieved and evils avoided, by, for example, killing a patient to relieve suffering, and not just killing non-combatants to destroy Nazi morale.

So the acceptance of the claim that there are moral absolutes makes a stringent demand on our practical reason: violation of such absolutes is never to be considered a real option for action, whether in hypothetical scenarios scared up to induce conditional violations, or in our day-to-day life, faced with the myriad of temptations to which each of us is subject.