There are reasons why Reddit makes Ohanian love total strangers. Reddit has a well-deserved, if eclectic, reputation for charitable giving. Redditors raised $700,000 to send a bullied senior citizen on a vacation, $4,000 to send to correspondent Helen Thomas after she asked White House spokesperson Dana Perino pointed questions about torture, and over $200,000 for World Vision, Doctors Without Borders and Islamic Relief in a competition between "sub-reddits" focused on Christianity, atheism, and Islam. And Reddit is emerging as a significant political force on issues that concern the Internet, serving as breeding ground for a massive protest against Internet registrar Go Daddy over the controversial SOPA/PIPA legislation and recently promoting "Take Back the Fourth" rallies to oppose NSA surveillance.

But the interesting piece of Ohanian's comment is the idea that Facebook and Reddit operate in radically different ways. For many Internet users, "social networks" are sites that build online links between people who already know each other offline. This was an idea exemplified in early social networks like Six Degrees (named after the six degrees of separation concept promoted by Stanley Milgram) and used in Facebook, Linked In, and Google Plus. When you join Facebook, the service mines your email inbox for friends, then asks questions about your education and work history to identify other possible contacts. Who you know on Facebook closely parallels who you know in the real world -- according to a Pew study, only 7 percent of Facebook friends are people a user knows only in an online context.

Because social networks like Facebook are all about who you know, they tend to be obsessed with authenticated identities. From its roots on elite college campuses, accepting only users with .edu email addresses, Facebook has had a "real name policy," which allows the site to remove the accounts of users who are using pseudonyms, arguing that online behavior is better when people are required to own their words. Google has followed suit, urging users to use real names on Google Plus and on YouTube. (These policies have raised questions from the human rights community, which points out that activists using online tools have valid reasons to conceal their identities, as do youth exploring sensitive questions around gender and sexuality.)

Reddit, by contrast, doesn't care who you are or who you know offline. Reddit names are unconnected to real-world identities and it's commonplace for users to create "throwaway" accounts to reveal sensitive information. In this sense, Reddit is more like the pre-social media Internet, when a New Yorker cartoonist could reasonably joke "On the Internet, no one knows you're a dog."

Identity isn't the only way Reddit has learned from early Internet culture. While Facebook is organized around your friends, replicating your offline social network, Reddit is organized around topics. This is a model that parallels Usenet, the Internet's ur-social network, a set of distributed message boards that served as a foundational influence on many builders of the contemporary commercial Web. While Facebook reconnects you with people you knew in elementary school or worked with years before, Reddit introduces you to strangers who share a common interest in photography, "Game of Thrones" or European politics.