Evidence of Absence - "You Can't Prove A Negative"

"You Can't Prove A Negative"

In 1992 during a presentation at Caltech, skeptic James Randi uses the phrase "you can't prove a negative". He claims that he cannot prove a negative (such that telepathy does not exist), but he also argues that an individual who claims telepathy exists must prove so. He discusses that induction is often used as a mode of proving a thesis, but if an individual assumes that something is or is not, then the person must prove so. Further, as he says, he does not take an advocacy position, as a lawyer would. He says that he cannot prove that a negative is true, but he could attempt to use evidence and induction to support a claim that he is biased toward, such as a claim that something does not exist (ex. flying reindeer).

Philosopher Steven Hales points out that typically one can logically be as confident with the negation of an affirmation.

Hales says that if one's standards of certainty leads them to say "there is never 'proof' of non-existence", then they must also say that "there is never 'proof' of existence either". Hales argues that there are many cases where we may be able to prove something does not exist with as much certainty as proving something does exist.