In the early 1980s, as fears of nuclear war gripped the Cold War world, then-Harvard President Derek Bok asked several faculty members at Harvard Kennedy School to analyze the nuclear threat and to weigh the policy choices. Among the project leaders was Joseph Nye, who was already a prominent political scientist with nuclear policy experience at the State Department and National Security Council. Nye, who went on to serve as HKS dean and to win acclaim for developing the concept of “soft power,” is now a Harvard University Distinguished Service Professor, emeritus.  

That small Harvard team of scholars produced an influential book, Living with Nuclear Weapons, sparking an intense debate and angering nuclear abolitionists. In response, Nye wrote his own book, Nuclear Ethics, to look more closely at the moral, philosophical, and ethical issues of nuclear weapons. His core conclusion: With nuclear weapons evidently an irreversible reality, the biggest challenge is not to eliminate them but to lower the risk of their use. Drawing on the just war theory, he set out a 10-point agenda for “just deterrence.”     

One of the graduate students on the original project was Scott Sagan, who went on to become an authority on nuclear weapons policy and is now co-director of the Center for International Security and Cooperation at Stanford University. Sagan recently asked Nye to look back at his 1986 book given the evolution of nuclear weapons technology, artificial intelligence, and proliferation threats. 

Nye’s reflection, “Nuclear Ethics Revisited,” was published in April in the journal Ethics & International Affairs. He concludes that while much has changed in the world since the Cold War, “the basic usability paradox of nuclear deterrence remains the same. As do the ethical dilemmas.” 

Nye answered questions about his thinking then and now on managing the threat of a nuclear war. 


Q: Why is this issue of nuclear weapons ethics worth revisiting nearly 40 years later? 

What the American Catholic bishops said in the 1980s remains true today: “We are the first generation since Genesis with the capability to destroy God’s creation.” While some political leaders like President Obama have spoken about a future world free of nuclear weapons, he acknowledged that we were unlikely to see it in our lifetimes. How to handle nuclear weapons is an unavoidable question.  


Q: What factors have changed? Isn’t nuclear weapons technology basically the same?  

The structure of world politics is different. The bipolar Cold War is over and has been replaced by a new great power competition that involves both a revanchist Russia and the rise of China. Russia invaded Ukraine in 2014 and 2022, seizing territory, threatening basic UN norms, and used nuclear threats to try to deter Western response. Brandishing nuclear weapons for political effect goes all the way back to Khrushchev, but the personality of Vladimir Putin is a new factor. Some commentators have argued that we are entering a “new nuclear age.” In addition, technology has changed with the internet, artificial intelligence, and cyberattacks, creating new problems for command and control. Complexity has grown, and with greater complexity comes a greater prospect of accident. The number of nuclear warheads has declined from some 50,000 to about 13,000 today, but countries continue to modernize their forces, and arms control treaties are being challenged. 

Joe Nye.

“If I put a sign on my front door saying, “No Elephants,” and there are no elephants in my house, did I deter them? It depends on the likelihood of literate elephants entering in the first place.”

Joseph Nye

Q: You developed a theory or doctrine of “just deterrence” in the original book. Is that still the right lens to use in considering this question? 

The basic nuclear dilemma has not changed. Nuclear deterrence has contributed to the longest period of non-war among great powers since the development of the modern state system. In the book, I likened nuclear weapons to a crystal ball and argued that if the leaders in August 1914 had peered into something like that and seen a picture of 1918 with tens of millions dead, four empires destroyed, and their removal from their thrones, we might not have had World War I. But crystal balls can be shattered by accident or sloppy handling. The heart of the nuclear deterrence dilemma remains the usability paradox. To deter, there must be some prospect of nuclear use, either deliberate or an accident that leaves something to chance. But how much usability is necessary for credibility? The greater the prospect of use, the greater the chance that the crystal ball will drop or slip out of human hands. And the greater the nuclear stability, the greater the risk of conventional instability (other things being equal). This basic problem has not changed much since I wrote in the 1980s. 


Q: Why is it helpful to go beyond moral intuition to try to develop a framework for moral reasoning about nuclear weapons use and deterrence? 

When many of us assess morality, we care about three things: the motives and intentions of the actors; the means they use; and the consequences they produce. In situations of good intentions, the hard cases involve trade-offs between means and consequences. There is no simple formula that guarantees good policy. Moral integrity comes from the quality of moral reasoning and the procedures that go into weighing such choices. My four principles for judging moral integrity include: 1. Clarity, logic and consistency; 2. Procedures for protecting impartiality; 3. Initial presumptions in favor of rules and rights; 4. Prudence in calculating consequences. When an expected consequence depends on a long chain of uncertain events, we must expect the unexpected and require a reasonable prospect of success before acting.  Failure to do such due diligence is culpable negligence. Ethical theory cannot be rounded off and made complete and tidy. As [political theorist and philosopher] Isaiah Berlin once wrote, “since the ends of men are many, and not all of them are in principle compatible with each other, then the possibility of conflict—and tragedy—can never wholly be eliminated from human life, either personal or social.” That is the human condition, but it does not exempt us from making difficult moral choices as we formulate policy. When I was in government, a French diplomat once told me that ethical questions were too vague and impossible to handle, so the only thing he considered was the interests of France. He seemed unaware this was itself a profound moral decision. 

Joe Nye speaks at a panel titled Education for Action in a Nuclear World
Joe Nye speaks at a panel titled Education for Action in a Nuclear World.

Q: How does the Ukraine war play into this ethics debate? 

In December 2021, President Joe Biden warned Russian President Vladimir Putin that Russia would face severe new sanctions if he invaded Ukraine, to no avail. Then, when the United States and its European allies thwarted Russia's plans by providing arms to Ukraine, Putin brandished the nuclear option, but Western aid continued unabated. Did deterrence fail or succeed? Answering this question poses a challenge because it requires assessing what would have occurred absent the threat. It is hard to prove a negative. If I put a sign on my front door saying, "No Elephants,” and there are no elephants in my house, did I deter them? It depends on the likelihood of literate elephants entering in the first place. The Ukraine war demonstrates how risk reduction is not always an either/or choice, but often a matter of degree. Perhaps Putin, counting on a flimsy Western alliance, believed the sanctions would fail. But he has so far refrained from striking supply lines in NATO countries. And while the West, for its part, has supported Ukraine, it has resisted supplying weapons that can hit Russia. Prudence remains a key virtue.  


Q: How does a rogue player like North Korea figure into the ethics question? 

North Korea violated its pledge under the Non-Proliferation Treaty and became the ninth country to possess nuclear weapons. The Kim regime regards them as essential to its claims to power both internally and externally. One should not expect the North Koreans to be bound by norms, but there are indications that they calculate their policies rationally.

Banner image by Jung Yeon-Je/AFP

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