> I’d like to understand the defining characteristics of social media platforms that contrasts them from traditional public forums that have existed through history.

I'll put out some ideas quickly. You can build on them. Please share back what you find.

Social media platforms, more or less:

* Tend to blur any one sense of place

* Offer geographically dispersed communication

* May deemphasize the overall humanity of participants

* Tend to accentuate particular aspects of people, such as photos or messages or resumes

* Offer asynchronous communication

* Allow for nearly zero-cost message sending and replication (i.e. retweeting)

* Unlimited person-to-person communication channels

Traditional town squares, more or less:

* Offer a tangible sense of place

* Offer a tangible connection to other people

* Are subject to public assembly laws.

* Only a limited number of people can fit.

* Public many-to-one communication is constrained by acoustics.

* So audio amplification is often needed.

* Private communications tend to be limited to short-range communication. In other words, you can't have N^2 two-person conversations.