The Invisible Pink Unicorn (IPU) is the goddess of a parody religion used to satirize theistic beliefs, taking the form of a unicorn that is paradoxically both invisible and pink. This makes her a rhetorical illustration used by atheists and other religious skeptics.
The IPU is used to argue that supernatural beliefs are arbitrary by, for example, replacing the word God in any theistic statement with Invisible Pink Unicorn. The mutually exclusive attributes of pinkness and invisibility, coupled with the inability to disprove the IPU's existence, satirize properties that some theists attribute to a theistic deity.
The IPU seems to have become notable primarily through online culture: in addition to alt.atheism, where IPU still frequently comes up in discussions, there are now a number of web sites dedicated to her. The earliest known written reference to the IPU was on July 7, 1990 on the Usenet discussion group alt.atheism. Other sources concerning IPU state that she was "revealed to us" on alt.atheism.
The concept was further developed by a group of college students from 1994 to 1995 on the ISCA Telnet-based BBS. The students created a manifesto that detailed a nonsensical (yet internally consistent) religion based on a multitude of invisible pink unicorns. It is from this document that the most famous quotation concerning IPUs originated:
"Invisible Pink Unicorns are beings of great spiritual power. We know this because they are capable of being invisible and pink at the same time. Like all religions, the Faith of the Invisible Pink Unicorns is based upon both logic and faith. We have faith that they are pink; we logically know that they are invisible because we can't see them." — Steve Eley
In 2007, Niamh Wallace wrote that the IPU had gained underground ubiquity as a symbol of atheism.
It is common when discussing the Invisible Pink Unicorn to point out that because she is invisible, no one can prove that she does not exist (or indeed that she is not pink). This is a parody of similar theistic claims about God—that God, as creator of the universe, is not subject to its laws and thus not materially detecting him tells us nothing about his existence or lack thereof. (It has likewise been said that trying to find God is like using a metal detector to search for unicorns in one's sock drawer.) The Invisible Pink Unicorn is an illustration which attempts to demonstrate the absurdity of citing attributes and a lack of evidence as proof of a deity's existence. Her two defining attributes, invisibility and color (pink), are inconsistent and contradictory; this is part of the satire. The paradox of something being invisible yet having visible characteristics (e.g., color) is reflected in some East Asian cultures, wherein an "invisible red string" is said to connect people who have a shared or linked destiny.
There are humorous mock-serious debates amongst her "followers" concerning her other attributes, such as whether she is completely invisible, or invisible to most, but visible to those who have faith in her (bearing similarities to "The Emperor's New Clothes"). Some of these debates are quite elaborate and tortuous, satirizing the disputatiousness and intricacy of many religions' theological debates.
"For I did see my unworthiness in Her sight, for I was a sinner, destined forever to spend existence in the presence of the unholy Purple Oyster, waxing his shell and massaging his most wretched and slimy feet. For lo, the Purple Oyster doth truly have feet, and the legs thereof, and the toes thereof, giving him dominion over all the clams of the seas, and allowing him to go unto the children of men, and tempt them unto destruction." — The Revelation of St. Bryce the Long-Winded (Partial), Chapter One, Verses 9 to 11
In 1996, a unicorn that no one can see was adapted as a teaching device at Camp Quest, the first free-thought summer camp for kids established in the United States, by Dr. L. Wilson. As reported years later in the July 21, 2006 Cincinnati Enquirer, "Campers must try to prove that imaginary unicorns—as a metaphor for God—don't exist." Richard Dawkins alluded to unicorns in this connection in his 2006 book The God Delusion, writing that "Russell's teapot, of course, stands for an infinite number of things whose existence is conceivable and cannot be disproved. [...] A philosophical favorite is the invisible, intangible, inaudible unicorn."
In Carl Sagan's essay The Dragon in my Garage from his book The Demon-Haunted World: Science As A Candle In the Dark, Sagan uses the example of an invisible dragon breathing heatless fire that someone claims lives in his garage. The supposed dragon cannot be seen or heard or sensed in any way, nor does it leave footprints. We have no reason to believe this purported dragon exists. This raises the question: How does the claimant know that this is a dragon, rather than, for instance, a cat? For that matter, how can we know that the IPU is pink and has one horn instead of three horns, or none at all?