Marshall and Eric McLuhan argued that an emerging medium is best understood by considering four questions or probes. They called these four questions the Laws of Media. Every new medium extends some capability, turns into its opposite if it grows too much, pushes aside other media, and retrieves some long lost activity from humanity's past. Exploring these four probes creates a kind of cognitive anti-environment, wherein the background become more evident and the medium can be better understood.

I think this might serve as a useful framework for thinking about twitter. Here is my cut at it.

What does the medium extend, enhance, intensify, accelerate or enable?

• Conversation with neighbors and casual acquaintances
• Announcements to a 'local' community
• Times Square

When pushed beyond the limits of its potential what does the new medium reverse into?

• Television when it was at its most mind-numbing
• Time's Square on LSD
• Stalking

What is pushed aside by the new medium?

• Postcards announcing programs and events
• Bulletin boards and posters
• Diaries and journals
• Gathering around a coffee pot at work

What does the new medium retrieve from the past that had been formerly obsolesced?

• Chatting over the back fence or rocking on the front porch
• Town criers
• The commons with its soapboxes and spontaneous retorts
• Times Square in the 1980s

Marshall McLuhan and Eric McLuhan, Laws of Media: The New Science, Toronto: University of Toronto Press, 1988.

Mark Federer, How to Determine the Business You're Really In.