When atheists say they need proof to accept the existence of God, what kind of proof do they want? People use words such as “proof”, “evidence”, “reason”, and “argument” to mean something real, sensible, perceptible, reliable, and testable.

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Atheists think they’re smarter than theists, so when they say things like this it’s less of an actual invitation for someone to trot out proofs and logic and more of a “here kid, take this toy car and go play while the adults are talking,” sort of dismissal. They don’t expect any kind of real answer to the question because they don’t think there could ever be a real answer to the question.