Poe's law, named after its author Nathan Poe, is an Internet adage reflecting the idea that without a clear indication of the author's intent, it is difficult or impossible to tell the difference between an expression of sincere extremism and a parody of extremism.
The law and its meaning 
Poe's law, in broader form, is:
The core of Poe's law is that a parody of something extreme by nature becomes impossible to differentiate from sincere extremism. A corollary of Poe's law is the reverse phenomenon: sincere fundamentalist beliefs can be mistaken for a parody of those beliefs.
The statement called Poe's law was formulated in 2005 by Nathan Poe on the website christianforums.com in a debate about creationism. The original sentence read:
8. Avoid sarcasm and facetious remarks.Without the voice inflection and body language of personal communication these are easily misinterpreted. A sideways smile, :-), has become widely accepted on the net as an indication that "I'm only kidding". If you submit a satiric item without this symbol, no matter how obvious the satire is to you, do not be surprised if people take it seriously.
Another precedent posted on Usenet dates to 2001. Following the well-known schema of Arthur C. Clarke's Third law, Alan Morgan wrote: "Any sufficiently advanced parody is indistinguishable from a genuine kook."
- Aikin, Scott F. (January, 23 2009). "Poe's Law, Group Polarization, and the Epistemology of Online Religious Discourse". Social Science Research Network. SSRN 1332169.
- Chivers, Tom (Oct 23. 2009). "Internet rules and laws: the top 10, from Godwin to Poe". The Telegraph.: "Without a winking smiley or other blatant display of humour, it is impossible to create a parody of fundamentalism that someone won't mistake for the real thing."
- "Big contradictions in the evolution theory". christianforums.com. Aug 11, 2005. Retrieved August 20, 2011.
- "Emily Post for Usenet". November 1, 1983. (Emily Post)
- "Bush's testing plan.". February 1, 2001.