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In 1917, a Philly police officer who’d infiltrated a Socialist Party meeting set off a string of events that would bring about a landmark civil liberties decision.

The famous metaphor about the potential danger posed by shouting “fire” in a crowded theater came from a case stemming from those events, in the opinion written by Justice Oliver Wendell Holmes — who eventually became an unlikely champion of free speech.

Here’s the thread explaining how it all went down.

Avi Wolfman-Arent is co-host of Studio 2 and a broadcast anchor on 90.9 FM. He was previously an education reporter with WHYY, where he's worked since 2014. Prior to that he covered nonprofits for the...