When a term is defined by reference to a proposition, the agent noun derived from that term must be defined in terms of belief in that proposition.

If, however, “agnosticism” is defined as a proposition, then “agnostic” must be defined in terms of “agnosticism” instead of the other way around. Specifically, “agnostic” must be defined as a person who believes that the proposition “agnosticism” is true instead of “agnosticism” being defined as the state of being an agnostic. And if the proposition in question is that neither theism nor atheism is known to be true, then the term “agnostic” can no longer serve as a label for those who are neith