In response to the utilitarian school of ethics, people often object that it is impossible to measure happiness, or to weigh the interests of two or more different sentient beings. A previous essay addresses this objection in brief; this essay will examine the issue more deeply.
Even if we cannot evaluate happiness, this in no way invalidates the principle of utility. If I lose the ability to perceive other people, they do not cease to exist; similarly, if I cannot perceive others’ happiness, their happiness still holds importance. It would indeed be tragic if we had no way of knowing how our actions affect others, but if this were the case, it would not constitute an argument against utilitarianism. At best, it could serve as a case for ethical egoism as the best method of increasing utility (see Argument 3 in “Using Utilitarianism to Argue Against Utilitarianism.”)
Fortunately, we know a good deal about how our actions affect others. While we cannot precisely feel what another person feels, we can make inferences as to others’ internal states. Animals (human and non-human) communicate their feelings and preferences through their behavior: if you step on a cat’s tail, it cries out and darts away from you. This indicates that it strongly prefers to avoid having its tail stepped on.
Of course, a rock may roll downhill, but is this because it desires to be at the bottom of the hill? Indeed, if you drop a cat off a building it will fall, but is this because it desires to reach the ground? No, because these actions are not voluntary. A cat cries out intentionally or instinctively to express its pain. Some plants let out distress calls when damaged, but this does not indicate pain because plants do not possess consciousness or the capacity to feel pain. It is unclear where the line lies between an unconscious reaction as an evolutionary adaptation and a conscious response to pain, but it is clear that vertebrates feel pain and plants do not. Do insects feel pain or pleasure? Maybe. But the only important facts for the purposes of this argument are that many animals suffer, and they express their suffering in a manner that we can observe.
We can indirectly infer the internal states of others–not just pain, but every emotion on the spectrum. As social creatures, we have evolved to perceive each other’s feelings. We can gain knowledge as to what sorts of actions promote well-being and use this knowledge to increase the total happiness in the world.
John Stuart Mill responds to a related objection in his definitive work, Utilitarianism:
Again, defenders of utility often find themselves called upon to reply to such objections as this- that there is not time, previous to action, for calculating and weighing the effects of any line of conduct on the general happiness. This is exactly as if any one were to say that it is impossible to guide our conduct by Christianity, because there is not time, on every occasion on which anything has to be done, to read through the Old and New Testaments. The answer to the objection is, that there has been ample time, namely, the whole past duration of the human species. During all that time, mankind have been learning by experience the tendencies of actions; on which experience all the prudence, as well as all the morality of life, are dependent. People talk as if the commencement of this course of experience had hitherto been put off, and as if, at the moment when some man feels tempted to meddle with the property or life of another, he had to begin considering for the first time whether murder and theft are injurious to human happiness. Even then I do not think that he would find the question very puzzling; but, at all events, the matter is now done to his hand.
Each individual person has spent considerable time learning what makes others feel pleasure and suffering, both through personal observation and through instruction. Parents teach their children how to respect others; “respect others” is another way of saying “do not cause others to suffer.” And throughout our lives, we learn through experience what sorts of behaviors promote others’ well-being. We learn to consider others’ interests and act to help others rather than hinder them.
And most of us become very good at it. You not only know what makes humans in general happy, but you know specifically what to do to make your mother happy, or your brother, or your husband. Perhaps your mother particularly dislikes when you chew your food loudly, or your husband greatly enjoys foot rubs. We accumulate such knowledge about our friends and relations, and can use it to increase utility.
We can also increase the well-being of those people with whom we do not have close relationships. Most people share certain tendencies as to what promotes their happiness. For example, nearly everyone dislikes physical pain ; so if I see a complete stranger who is about to walk through poison ivy, I can redirect her and feel confident that I have helped her. There is a small chance that she enjoys feeling poison ivy on her skin, but that is a risk worth taking.
Although we cannot be absolutely certain that a particular action will increase utility, absolute certainty is not necessary. Indeed, we cannot be absolutely certain about any empirical question. Gravity may cease to work tomorrow, but we still behave as though it will continue the way it has. We can make educated guesses as to what will increase utility and we will be correct most of the time.
Some may object that we cannot precisely measure happiness, and thus cannot weigh one person’s well-being against another’s. While there are limits to our capacity to measure happiness, we can indeed measure it (as discussed above), and some sorts of preferences clearly outweigh others. My personal desire to avoid significant injury outweighs my desire to shoot someone in the leg for fun (I do not happen to desire this at all, but suppose I did for the sake of argument); from this, and from my knowledge of other people’s desires, I can infer that another person’s preference to avoid injury outweighs my preference to shoot him for fun. In other words, the happiness I might gain from shooting someone pales in significance to the suffering he would experience if he sustained a major leg injury.
Some cases less clearly reveal which action best increases utility, and such situations are the source of much debate. For instance, does raising taxes on the wealthy improve the general welfare of society? We do not know the answer, but we do have evidence that points one direction or the other and we can collect still more evidence so as to better answer the question. However, irrespective of such cases, in many situations we can clearly observe that one choice increases utility to a greater extent than another. Additionally, people make many choices that clearly decrease utility, and we can improve the world by altering such choices.
Recently, science has begun to directly investigate the question of what makes us happy. Every day, the science of positive psychology wades deeper into the sea of human happiness, and we learn more and more. Many popular science articles have been written on the subject. The field is still in its early stages, but as it develops, I think we will become very good at scientifically measuring happiness.
We know, for example, that many small experiences make people happier than a few big experiences. Money brings happiness up to a certain level of income, and then plateaus. Science has provided many insights into happiness, and will continue to do so. Indeed, this is the thesis of Sam Harris’s recent book, The Moral Landscape.
Science tells us much about how to increase utility. But to effectively support the well-being of our communities, we must understand how our actions affect others on a personal level. Empathy is one of our best tools for this. When we can comprehend others’ positions, we can act in ways that support their interests. Empathy is the primary means through which we understand what makes others happy. If someone claims that we do not know how to make each other happy, she must claim that we have no empathy.
We can measure the well-being of the people around us, whether through science or through our personal capacity for empathy. We cannot measure happiness precisely, but we still know what sort of impact our actions have on the emotional states of those around us.
 It may seem that physical pain decreases utility by definition, but this is not so. It is important to distinguish between suffering and physical pain. Suffering _does_ necessarily decrease utility, but some forms of pain are enjoyable. For instance, stretching one's muscles hurts, but that hurting often brings pleasure--it hurts "in a good way."
Masochists get pleasure out of physically painful experiences that cause most people to suffer. It is not inconsistent with the idea of utilitarianism to inflict physical pain upon a masochist.