Here's the breakdown of its origin:
* Early usage: The phrase likely evolved from ancient proverbs highlighting the absurdity of impossible scenarios.
* First recorded usage: The exact origin of this particular idiom is unclear, but it's been used in English for centuries. It appears in writing as early as the 18th century.
* Metaphorical meaning: The absurdity of pigs flying stems from their natural inability to do so. It became a way to express that something was so unlikely, it might as well be impossible.
Similar expressions:
* When pigs fly: This is a slightly more common variation.
* When hell freezes over: This phrase conveys the same idea of something being highly unlikely.
* You'll see pigs fly before that happens: This variation emphasizes the extreme improbability of the event.
These idioms are all examples of hyperbole, using exaggeration to emphasize a point. They convey the message that something is very unlikely to occur, and are used in a humorous and informal way.