Some of us welcome the prospect of a future in which technology continues to change our minds and bodies, expanding our choices and capabilities. But that is not a universally accepted view. There are many opponents who concentrate on the possible abuses (as they see them) of enhancement technologies and suggest that a future in which we increasingly overcome our biological limitations will be a terrible time to live.

An initial response to them is that our descendants (or we, ourselves, if any of us live that long) may well be happy in a future society of technologically enhanced people. Indeed, humans of the future will probably recall our time as a relatively primitive one that they would never choose to revisit. Gregory Stock has made the point well in his book Redesigning Humans. "A thousand years hence," he writes, "those future humans—whoever or whatever they may be—will look back on our era as a challenging, difficult, traumatic moment. They will likely see it as a strange and primitive time when people lived only seventy or eighty years, died of awful diseases, and conceived their children outside a laboratory by a random, unpredictable meeting of sperm and egg."

Plausible though this is, it is not the end of the story. Even if future humans prefer their society and way of life to ours, will they be right to do so?

Brave New World revisited

Most of the characters in Aldous Huxley's Brave New World consider themselves happy and would not prefer life in any previous society. Their lives are subjectively pleasant, and whatever desires they feel are satisfied—almost without a glitch. As with the future humans imagined by Stock, the inhabitants of Brave New World would be unimpressed by our society. They would be repelled by its instability, frustrations and endless sources of dissatisfaction.

Yet we find the world of Brave New World repugnant, and would do a great deal to prevent it from coming about. It seems clear that we cannot judge whether a society is good or bad merely by whether some or all of its inhabitants prefer to live in it, or even by whether their lives seem pleasant to them.

In the case of Brave New World, much of value is missing from people's lives. The society's creators and rulers have set out to maximize social stability. In doing so, they have banished suffering and frustration, but they have also ruthlessly cut out love, friendship, personal challenges, genuine art, most science and all but the most banal kinds of individual achievement.

What is flourishing?

Martha Nussbaum is one philosopher who expressly rejects the idea that what matters is simply the fulfillment by a society of its inhabitants' actual desires. As she points out in her article "Aristotelian Social Democracy," people with opulent lives may come to feel dissatisfied if they are deprived of that opulence, while people who live in severe deprivation often adapt to what they have, and come not to desire anything more. Rural women in third world countries may live with narrowed horizons of desire that they have internalized as "natural"—as may many women in Western society, even today. Other people come to accept horizons that have been narrowed by illness, disability, social class, family background and prejudice.

All too often, people's horizons narrow. Perhaps this is merciful to those who would otherwise be burdened by frustration, but we don't want to say that people are living flourishing human lives in those circumstances, not even if they profess to be happy.

When we make judgments about whether a real or imagined human society is good or bad overall, we should first consider whether its people are leading flourishing lives. In fact, we should be slightly more precise than this. No individual's flourishing can ever be guaranteed by the society as a whole, or by its political institutions, since so much depends on personal choices and an element of sheer luck. So we should judge past, contemporary or imagined human societies by the opportunities for flourishing that they offer—or deny—their inhabitants.

But what, exactly, is flourishing? So far, I have only defined it negatively: It is not to be found solely in subjective feelings of pleasure, or even in the satisfaction of preferences and desires. The idea is rooted in Aristotelian ethical and political philosophy, and the word "flourishing" is one way of translating the Greek word eudaimonia. This often appears in English translations as "happiness," but that is misleading to the extent that eudaimonia refers to a life's going well, not just to subjective feelings of pleasure.

Nussbaum develops a fleshed-out conception of a flourishing life for human beings, applicable across all cultures and societies. Central to her theory is the claim that we should ask what people are actually able to do in the society in question and, indeed, what they are actually able to desire. As she writes, "We consider not only whether they are asking for education, but how they are being educated; not only whether they perceive themselves as reasonably healthy, but how long they live, how many of their children die, how, in short, their health is."

Basic capabilities

The picture that emerges is that we are beings situated "between the beasts and the gods." We have some abilities that distinguish us from the nonhuman natural world, yet we are part of nature, and that sets limits to our powers.

According to Nussbaum, we are beings who are mortal but have an aversion to death. We live in bodies of a certain sort, which have much in common, despite superficial differences in appearance. We have bodily needs or fundamental desires, such as for food and drink, shelter, sex, and movement. We have capacities for pleasure and pain, and an aversion to pain as "a fundamental evil." We have cognitive capacities—those which relate to perceiving, imagining and thinking. We also have a common experience of helplessness early in life.

We are individuals but also social animals. We participate in planning our lives, questioning what is good and how to live, and we want to enact our thoughts on this in our lives; but we also affiliate with others in relationships of love, kinship, friendship and alliance. We recognize a relationship to other species and to nature. We want a life with recreation, play and laughter. Despite our social nature, we are separate from each other, not fused together. Indeed we possess and value what Nussbaum calls "strong separateness"—we say that some things are "mine," and we each do things from our own separate point of view.

Based on these considerations, Nussbaum offers an extensive list of human capabilities:

* Being able to live to the end of a complete human life, as far as is possible; not dying prematurely.
* Being able to have good health; to be adequately nourished; to have adequate shelter; having opportunities for sexual satisfaction; being able to move about from place to place.
* Being able to avoid unnecessary and non-useful pain, and to have pleasurable experiences.
* Being able to use the five senses; being able to imagine, to think and reason.
* Being able to have attachments to things and persons outside ourselves; to love those who love us, to grieve at their absence; in general, to love, grieve and to feel longing and gratitude.
* Being able to form a conception of the good and to engage in critical reflection about the planning of our individual lives.
* Being able to live with concern for and in relation to animals, plants and the world of nature.
* Being able to laugh, to play, to enjoy recreational activities.
* Being able to live our individual lives and nobody else's.
* Being able to live our individual lives in our very own surroundings and contexts.

In Nussbaum's thinking, many of these capabilities overlap and interact, but they are all basic, and a life lacking in any of them, or deprived of opportunities to exercise them, would be an impoverished one for a human being.

Beyond happiness

Once we begin to spell out in so much detail what constitutes a flourishing life, where do we stop? We run the risk of being either overly prescriptive or of leaving something important out of what is intended to be a comprehensive list. I'm sure that the precise list offered by Nussbaum could be modified or manipulated to suit the values of individuals, and there is a temptation to use it paternalistically, telling people exactly what desires they should have and what capabilities they should be exercising, even though their actual desires and choices about how to live might differ from ours, and might not have been distorted in any significant way (e.g. by social conditioning, accommodation to poverty, etc.).

I doubt that we could ever develop a list of essential human capabilities that is totally definitive and uncontroversial. Nonetheless, Nussbaum's attempt shows that there is much in a full human life that goes beyond merely being superficially "happy." Furthermore, her strong emphasis on our separateness is a barrier against inappropriate paternalism, because it makes clear that we are all different and will legitimately wish to pursue many specific, and perfectly acceptable, plans of life.

At the least, such an analysis reminds us that we value a society in which people have opportunities to live rich, full lives with many dimensions to them, hindered by neither unnecessary social constraints, nor economic scarcity, nor psychological accommodation to narrowed horizons.

Encouraging variety

It is one thing to make a list of human capabilities and to use them as an indication of the dimensions of a flourishing human life. But what would be a flourishing life for someone whose capabilities were greater than those possessed to date by human beings? How should we judge a society of future humans who might actually be, in some ways, more than human?

Some passages in Nussbaum's work give the impression that she might be hostile to human enhancement—though as far as I am aware, she has not addressed the issue directly. She certainly argues in many of her publications that the lives of immortal, invulnerable, godlike beings, or of souls in a transcendent Platonic or heavenly realm, would be missing much that we consider valuable.

Even if that is accepted, however, it does not necessitate that we abandon the quest to enhance our cognitive and physical abilities. No matter how much we succeed in enhancing ourselves, we will remain between the animals and imagined transcendent beings. If our capabilities increase, that will not prevent us from leading flourishing lives, though our flourishing will require the exercise of our new or augmented capabilities. If, for example, our cognitive abilities are amplified, we will need projects and activities that challenge them.

It is in our nature to struggle against our limitations, even if there might be a downside to total success. Nussbaum is doubtless correct that we would not prefer a life without, say, hunger to one with both hunger and food. We might not prefer a life of godlike transcendence if we had it, but we have every reason to seek longer and healthier lives than we currently have, including by increasing our bodies' resistance to aging and disease.

Some transhuman futures that we can imagine are, indeed, repugnant to us. A society in which most people were restricted in their choices and activities, and in the horizons of their desires, would clearly be a bad one. Such a society might well emerge if opportunities for cognitive and physical enhancement were monopolized by a self-perpetuating overclass of the rich.

However, we need not allow that to happen. We should prevent such a society coming into existence, not by suppressing enhancements of our capabilities, but by ensuring that enhancements become widely available, not restricted to a privileged class. That will involve favoring enhancements that can become common in future societies, which will probably mean, in turn, encouraging those enhancements that could assist people in a wide variety of life plans.

If we adopt that principle, we can welcome human enhancement, aiming for a future society whose inhabitants can lead flourishing lives of unprecedented scope and capability.