Skepticism about morality in foreign policy is common among foreign policy analysts. As one scholar described graduate training in international relations, "Moral argument was against the rules of the discipline as it was commonly practiced."

The reasons for skepticism seem obvious. International relations are the realm of self-help and survival. Realist diplomats such as George Kennan－the father of the containment theory during the Cold War－have long warned about the bad consequences of the US' moralist-legalist tradition. International relations are the realm of anarchy with no world government to provide order. States must provide for their own defense, and when survival is at stake, the ends justify the means.

Where there is no meaningful choice there can be no ethics. No one can fault you for not doing the impossible. By this logic, combining ethics with foreign policy is a mistake, and in judging a foreign policy we should simply ask whether it worked. A French official once told me that morals are irrelevant in international politics; only the interests of France matter. But I do not think he realized what a profound moral judgment he was making by ignoring the interests of others.

The skeptical view ducks hard questions by oversimplifying. Some foreign policy issues relate to survival as a nation, but most do not. Many important foreign policy choices about human rights or climate change or internet freedom or pandemics do not involve war at all. Most foreign policy issues involve trade-offs that require choices among values. And standing for values can enhance a country's soft power－the ability to influence others by attraction rather than coercion or payment. A cynical official once said that in international politics, interests bake the cake and then politicians merely sprinkle a little moral icing on it to make it look pretty. But it is tautological or at best trivial to say that all states try to act in their national interest. The important moral question is how leaders choose to define and pursue national interests under different circumstances.

Some hard-core skeptics contrast values with interests, but that is a false dichotomy. Our values are among our most important interests because they tell us who we are as a people. Like most people, US people care more about their co-nationals than about foreigners, but that does not mean they are indifferent to the sufferings of other humans. Few would ignore a cry for help from a drowning person because the call for assistance is in a foreign language. Of course, US presidents are constrained by public opinion in a democracy, but they often have considerable leeway to shape policy, and far-sighted leaders understand that our values can be a source of soft power when others view our policies as benign and legitimate.

For better and worse, US people constantly make moral judgments about presidents and foreign policy, but many of their judgments about ethics and foreign policy are poorly thought through. We are often unclear about the criteria by which we judge a moral foreign policy. A president such as Ronald Reagan is praised for the moral clarity of his statements as though rhetorical good intentions are sufficient in making ethical judgments. However, Woodrow Wilson and George W. Bush showed that good intentions without adequate means to achieve them can lead to ethically bad consequences, such as the failure of Wilson's Treaty of Versailles or Bush's invasion of Iraq. Or a president is simply judged on results, such as Richard Nixon ending the Vietnam War, which overlooks the fact that he sacrificed 21,000 US lives to create a reputational "decent interval".

In my book Do Morals Matter? Presidents and Foreign Policy from FDR to Trump, I argue that good moral reasoning should be three-dimensional, weighing and balancing the intentions, the means, and the consequences of decisions. A moralistic foreign policy is not a matter of intentions versus consequences but must involve both as well as the means that were used. Moreover, good moral reasoning must consider the consequences of general actions such as maintaining an institutional order that encourages moral interests, as well as particular newsworthy actions such as helping a human rights dissident or a persecuted group in another country.

The book presents summary "report cards" on the 14 US presidents since 1945 after balancing their intentions, the means they used and the consequences they produced. Not everyone might agree with the scoring, and as time goes by and historians learn more, even I might want to change some of the scores I have given. As Henry Kissinger once noted, the hardest foreign policy decisions are often very close calls. But my purpose is not to assign scores for all times or just for US presidents, my aim is to help people make their own careful judgments about ethics and foreign policy. Since we are going to use moral reasoning for foreign policy, we should learn to do it better.

Prudence is an important instrumental value for a moral foreign policy. Prudence exercised by both countries will be important to managing the "cooperative rivalry "of US-China relations over the coming decades. There are bound to be differences over both values and interests between the two countries, but failure to manage the relationship carefully would lead to high immoral consequences for everyone.

The author is a professor at Harvard University and author of Do Morals Matter. Presidents and Foreign Policy from FDR to Trump. The author contributed this article to China Watch, a think tank powered by China Daily. The views do not necessarily reflect those of China Daily.