Utilitarian and deontological reasoning have very little in common. They are similar in that they are both concerned with trying to determine what human actions are right and what actions are wrong. Beyond that, however, there are no similarities. They are very different because they take very different approaches to understanding what is good and what is bad.
Utilitarian reasoning is “consequentialist.” That means that it bases its judgments on the consequences of a person’s actions. In this view, an action is good or bad because of how it turns out. Its morality has nothing to do with what the person meant to do. To take an extreme example, imagine that I am driving along and I see someone that I hate who is walking along on the sidewalk. I decide to run him over with my car. He sees me coming and dives out of the way. I accidentally run over someone behind him, who had an automatic rifle and was about to murder five people. According to utilitarianism, I have committed a good act because I saved the lives of five people. The fact that I saved them unintentionally while trying to kill someone else is irrelevant; all that matters is what came about because of my action.
Deontological reasoning takes the opposite approach. In this view of the world, our actions are good or bad because of why we do them. If we do things out of good intentions, our actions are morally good no matter what their results are. If we look at the scenario from the last paragraph from a deontological point of view, we would say that my action was wrong. When I drove my car up onto the sidewalk, I meant to kill an innocent person. The fact that I accidentally killed a bad person and saved lives has nothing to do with the morality of my action. My action was immoral because I was trying to do a bad thing.
Thus, these two types of philosophy are very different. Utilitarianism is concerned with how our actions turn out while deontological reasoning is concerned with the motives behind our actions.
We can make the distinction clearer with the aid of a thought experiment.
Imagine that you are asked by someone to shoot one person. If you do not do as you are asked, the person asking you to shoot that person will shoot fifteen other people. What should you do? What is the morally correct action?
Now the utilitarian is concerned solely with the outcomes or the consequences of the action. The right action is the one from which we may derive the most utility. Thus, a simple act utilitarian would say that you ought to shoot that one person, since one person dead is a better outcome than fifteen people dead. This way of thinking has its origins in John Stuart Mill’s On Utilitarianism.
The deontologist, on the other hand, might argue that one has a perfect duty to others not to kill them and the right action is one that involves fulfilling one’s perfect duties. This is the language used by Immanuel Kant in his Critique of Practical Reason. The deontologist would claim that one ought to do has nothing to do with the consequences of one’s actions.