According to Williams, in a post he published on the site Wednesday night, Medium is not a publishing tool—a statement that might confuse some of the writers who have been using it as exactly that for the past year or so, not to mention some of the staffers who have come to think of publishing as the core of what Medium does.

Certainly the earliest adopters of Medium did so because it was a great writing tool: the user interface when you author a post is excellent, an intuitive and easy-to-use series of features. It also allowed those without a personal blog to get “reach” by being promoted on the site by Medium editors and users. Along with LinkedIn, it has quickly become the default place for entrepreneurs and CEOs to write about themselves.

So if it’s not a publishing tool, then what is it? It takes Williams a little while to get to the point in his post, but in a nutshell it sounds like it’s a social network, or at least it wants to be one. Instead of long-form journalism, the focus is on interaction—which occurs in part through features like notes (Medium’s version of comments) and highlighting, but also through short responses to existing posts that are published and appear as their own posts, a la Tumblr or Twitter.

“In the last few months, we’ve shifted more of our attention on the product side from creating tool value to creating network value. What does this mean? Obviously, one form of that value is distribution… but the more interesting bit of network value we’re starting to see a lot more of is qualitative feedback.”

In this, the Medium founder’s thinking has pretty clearly been influenced by the contrast between his two most famous creations: Blogger was a great publishing tool, he says in his post, but it didn’t have enough social elements and so it failed to grow. Twitter, however, was all about the network effect; the actual writing and publishing tool was so small and inconsequential that it barely existed at all. The only important thing was the connection to and interaction with others on the network.

“My next ‘blogging’ tool had far fewer features — and way more users. No one moves where they tweet because some other tool has better formatting or profile customization. That’s because a tiny percentage of the value Twitter brings comes from the software itself. It’s all about the network — the connection with other users and the content they create.”

Medium has already made a number of changes in an attempt to become more Twitter-like: the service launched the ability to publish much shorter posts, with a lightweight, Twitter-style tool added to the homepage. And it also added support for tags, which would allow users to browse through topic-style feeds.

Transforming the service from being a kind of networked digital-magazine publisher into a social network is a tall order, however. In a piece at BuzzFeed, writer Charlie Warzel goes into some depth about the impact that some of the changes have had at Medium, including a shuffling of responsibilities related to some of the site’s “magazines” or collections, including Matter and The Message. Some staffers seem concerned that the new focus will mean more work and less reward.

What Medium is going through feels very much like what other media players are also struggling with: the Warzel piece talks about how Williams and editorial content head Evan Hansen are concerned about increasing engagement and getting users to log in more and interact—which also sounds very much like the challenge Twitter is facing.

The changes Medium is implementing seem designed to try and lower the barrier to participation with the site’s content. But will those changes just dilute the very thing that made Medium different from the rest of the marketplace? If nothing else, they will probably add fuel to the idea that what Twitter and Medium should do is merge, since they seem more and more like two different expressions of the same impulse (although Williams’ departure from Twitter was less than graceful).

Update: Evan Williams has followed up his original post on the site’s direction with another one in which he responds to some of the commentary about whether Medium is “pivoting” or not. He says the networked and discussion-oriented approach has always been part of the site’s road map.