But do these young people even know what they are missing? And does it matter?

Social isolation has certainly increased in Japan, where half a million young people live as “hikikomori” — recluses who don’t leave their homes . And loneliness in Britain has increased enough that the government has created a “minister for loneliness.” According to a new survey, 86 percent of American and British citizens believe that “increased use of technology” is contributing to social isolation.

Some of the earliest philosophical work on friendship comes from Aristotle, who pointed out in his “Nicomachean Ethics” that friendships of pleasure and utility are easily formed but also easily abandoned because such bonds are flimsy. Deep friendship, by contrast, is when you care for your friend for her sake, not for any benefit you can accrue from the relation. This is selfless friendship. You can have only a couple of these friends because they require a lot of time, work and effort, and a general blending or intertwining of two lives. You have to clock time with these people, and you must make sacrifices for each other.

Classmates and workmates can become friends, as can fellow members of sports teams and musical groups, spouses, religious or military colleagues, and so on. These examples suggest that friendship needs three criteria for full realization: shared experience, loyalty and shared intentionality, or mental connection.

What about in the digital sphere? Our online “friends” — whether it’s Scuzzball or the Facebook friend you’ve never met — satisfy the intentionality criterion, because we communicate extensively with language and report to each other long-term goals, disappointments, beliefs and other facets of mental life.

We can share experiences with a person online, but the experiences seem thin when compared with face-to-face experiences. Online adventures (social networking, gaming) can certainly strengthen friendship bonds that were forged in more embodied interactions, but can they create those bonds?

Teenagers playing “Call of Duty” with online teams, for example, are having collective emotional experiences, as in the case when my son’s squad must work to capture the enemy’s munitions. And these shared adventures strongly trigger the dopamine pleasure system, so it seems like there should be bonding. However, the online “friends” may be little more than dopamine-dosing tools and easily replaced without much dissonance. Indeed, one doesn’t even know who Scuzball is, or where he lives, or if he’s a he, or if he is a person or a bot.

The kind of presence required for deep friendship does not seem cultivated in many online interactions. Presence in friendship requires “being with” and “doing for” (sacrifice). The forms of “being with” and “doing for” on social networking sites (or even in interactive gaming) seem trivial because the stakes are very low.