Samuel Johnson's first dictionary of the English Language, published in 1755, gave the definition of swan as “The ſwan is a large waterfowl, that has a long and

Samuel Johnson's first dictionary of the English Language, published in 1755, gave the definition of swan as “The ſwan is a large waterfowl, that has a long and very ſtranght neck, and is very white, excepting when it is young [...]”, Following your logic, I have just proven that black swans do not exist.