How do you know mermaids are not real?

Answer 1

It is impossible to know if something is not real.

If I wanted to disprove the existence of mermaid what I would do would be to try and prove the existence of mermaids and fail. This is still not proof of their non-existence however. A critic of my efforts would only have to say that I did not look hard enough or in every possible location.

However, the case for the non-existence of mermaids is compelling. All "evidence" of mermaids that has been put up to scientific scrutiny has either turned out to be misinterpretation of ordinary marine organisms (such as dead stingrays), or deliberately faked. Additionally, humans and fish are separated by nearly 400 million years of evolution, and all humanoid characteristics evolved long after this split, so it is impossible for there to be a half-human half-fish.