The title of Robin Dunbar’s recently published book asks a good question: How many friends does one person need? (http://www.faber.co.uk/work/how-many-friends-does-one-person-need/9780571253425/)
Dunbar suggests that a human being can’t have more than about 150 friends (or ‘acquaintances’, as the book itself somewhat revealingly puts it). But of course it all depends on who we count as a ‘friend’. If we are talking about people with whom one spends a good deal of one’s time, then the number would usually be significantly lower; whereas if we allow friends to include what Aristotle called philoi, it could be much larger. People are philoi when they have some kind of goodwill to one another, and are mutually aware of that goodwill (Nicomachean Ethics VIII.2). On this generous view, even Facebook ‘friends’ one has never met might be genuine, if those extending and accepting the invitation do have some real concern for one another.
Aristotle’s profound and considered thoughts on friendship illustrate a conflict between two ideals: those of self-sufficiency on the one hand and community membership on the other. Solitary contemplation is the most self-sufficient of human activities, and indeed brings us closest to the divine. But human beings are political – that is, they live in poleis or cities – and the ideal human life will be one lived with parents, children, partner, and friends and fellow-citizens generally. So how many friends one needs will depend to some extent on one’s chosen mode of life. But we should not be over-impressed by the idea of the ‘solitary genius’. Even Simeon Stylites, who lived as an ascetic on his pillar for nearly forty years, allowed visitors to ascend his pillar, wrote letters, and gave lectures to the multitudes below.
The right number of friends also depends on what human well-being or happiness really consists in. On Aristotle’s view, happiness consists at least partly in the exercise of the virtues, and one will need friends as objects of and collaborators in one’s virtuous actions. And friends are often included in lists of allegedly objective human goods, alongside knowledge, accomplishment, and pleasure. But those who take a more subjective position – hedonists, for example – will see value in friendship only in so far as that friendship is something that brings some other benefit, such as enjoyment, to the friends. So friends whose company you no longer enjoy aren’t worth keeping.
Indeed some philosophers have gone so far as to suggest that friendship is positively bad, in its distracting us from the entirely impartial ‘point of view of the universe’, to use Henry Sidgwick’s phrase. In a world such as ours, where one can save someone’s eyesight for a few dollars, how can it be justifiable to spend time with close friends, let alone buy them gifts, when one could be putting one’s time and money into promoting the universal good? But it has to be said that such extreme views are rare. Even those who believe that ultimately what matters is the universal good recognize that any human being can effectively advance that good only with the psychological support of friends. Here friendship is not so much a constituent of virtuous activity as a necessary means to it.
Evolutionary theory, then, is only part of the answer to the question of how many friends we need, in so far as evolution puts certain constraints on what is possible. Also required is philosophical reflection on the nature of friendship, its role in human happiness, and the demands of morality.