By Stephen Nathanson

You may wonder where a philosopher like me goes to work “in the field." You may wonder where a philosopher like me goes to work "in the field."

In general, I don't have to go to a special location to conduct research. Anyplace where I can think, write, talk to people, and read what others have written will do. Unlike researchers in other disciplines, who often aim to discover what no one yet knows, philosophers often focus their attention on what we think we already know.

Since the September 11 attacks, I've focused my research on widespread beliefs about terrorism and the ethics of war. My first reaction to the attacks, like that of most citizens, was to conclude that terrorism is a serious evil and terrorist acts are always wrong. Although those beliefs seemed obvious to me, as a philosopher, I knew that they were more problematic than they initially seemed.

To explain why, I need to say something about the methods of philosophical analysis.

The basic methods of philosophy go back to the ancient Greek philosopher Socrates, who inspired some contemporaries-and irritated others-by constantly challenging them to define their terms and justify their beliefs.

He'd ask people questions like "What is justice?" or "What is courage?" Socrates thought you couldn't really know whether someone was just or courageous without being able to define those terms, or describe the qualities that make people just or courageous.

When people couldn't answer his questions-and they generally could not-Socrates would conclude they did not know what they were talking about. No wonder he was unpopular.

After 9/11, I started asking myself similar questions about terrorism. Though terrorism is something most of us readily condemn, we usually can't say what it is, or what makes it immoral. Even scholarly discussions about its nature are confused and contradictory. According to one scholarly article, there are over a hundred different definitions of terrorism.

In my research, the questions I seek to answer are, What, exactly, is terrorism? What makes it wrong? And, finally, are our answers about what makes terrorism wrong consistent with our other moral beliefs? My goal is to be able to give a clear account of the nature of terrorism, and a logically consistent, plausible set of reasons for condemning it morally.

To illustrate how I work, consider the view that what makes terrorism wrong is that it kills or injures people. It's a plausible response, but as an explanation it fails. It fails because it does not distinguish terrorism from other killings that most people believe can be morally justified. Anyone who believes that killing in self-defense or waging war can be morally justified cannot condemn terrorism simply because it kills or injures people.

Either we have to find other reasons that set terrorism apart and explain why it's always wrong. Or we must conclude that some acts we had previously thought to be morally right are actually wrong.

It would be easy to condemn terrorism and not condemn similar acts if we were under no obligation to be consistent. But any set of beliefs has to be consistent in order to be correct. A lack of consistency always undermines our logical and moral credibility.

Nevertheless, as we know, moral judgments about violence are often inconsistent. This leads some people to call any condemnation of terrorism hypocritical. They see that acts that are censured when they're performed by one group are often praised when they're performed by another. As the slogan goes, "One man's terrorist is another man's freedom fighter."

According to this slogan, there is no such thing as terrorism, because acts of violence are approved or disapproved on the basis of who does them, not on the basis of the action itself. Although there are certainly real acts of violence, the slogan says, whether they constitute terrorism is in the eye of the beholder.

I reject this view. I believe it's possible to define terrorism in a neutral way. According to my definition, terrorist acts are serious acts of violence that target innocent people and are performed in order to advance a political goal or agenda.

Applying this definition impartially can help us avoid the charge of hypocrisy. If we use the definition, we will label all serious acts of violence that intentionally kill or injure innocent people for the sake of a political goal as terrorism. If an ally of ours commits such actions, that ally will be committing terrorism. If "freedom fighters" or others pursuing some valuable goal kill or injure innocent people to achieve their goal, they are terrorists, too, even though their goal may be one that we approve.

In addition, if all acts of terrorism are wrong, then these acts will be wrong even if they are committed by our allies or ourselves, and even if they are done to achieve a valuable goal.

But the impartial labeling and judging of actions can raise other problems for us. We might find that the consistent labeling and judging of terrorist acts conflicts with other beliefs that we hold.

Suppose that we believe the highest duty of a country's leaders is to promote the national interest-to preserve the country's independence, for example, or protect its citizens' freedoms.

In addition, suppose that in some circumstances, the national interest could be promoted by actions that intentionally kill or injure innocent people. If so, then according to the "national interest is paramount" view, it would be right to kill innocent people.

Following this thinking, terrorist acts that promote the national interest would be morally justified. But if this is true, then terrorism is not always wrong. Unfortunately, we can now see a serious inconsistency in our beliefs. The belief that terrorism is always wrong, which we initially thought was obvious, conflicts with the belief that we should do whatever promotes our national interest, another belief that is also generally taken to be obviously true.

This quandary illustrates the sort of problem philosophers examine. People often find themselves in a position where they have good reasons for each of two beliefs, yet both beliefs cannot be true simultaneously.

Philosophical analysis helps us explore how to resolve these kinds of inconsistencies. In this case, we might decide that terrorism can sometimes be justified. Or, if we stick to the view that terrorism is always wrong, we would have to conclude that some actions are wrong, even if they promote our national interest.

We all engage in this kind of reflection from time to time. What sets philosophers apart is that we attempt to examine, clarify, and criticize beliefs as thoroughly and systematically as possible.

My own research goal is to work out a consistent and plausible set of moral principles that helps us judge acts of war and political violence. Because I believe that terrorism is always wrong, I want to work out the moral limits of what can be done in defense of the national interest, and this part of the work will inevitably be controversial.

As a philosopher, I know that when I present or publish my work, other philosophers will be assessing my conclusions very critically. So I have to examine my beliefs to spot any weaknesses or contradictions. And if I find that some of my beliefs are indefensible, then my commitment to truth should lead me to change them.

Stephen Nathanson is a professor of philosophy in the Department of Philosophy and Religion.