Proving too much
Proving too much is the logical fallacy of drawing a conclusion that is too broad, therefore conflicting with other propositions that are known to be true or conflicting with a logical prerequisite to the proposition itself. Generally, this arises when someone intentionally tries to sound intelligent but their vagueness betrays their lack of knowledge or expertise.
It can be summed up in the medieval adage, quod nimis probat, nihil probat: "what proves too much, proves nothing".
Most of these can be fixed by adding a qualifier or a self-exception.
- "Nothing can be known for certain."
- This proposition (otherwise known as Pyrrhonism) proves too much by casting doubts about itself, because the truth about the statement itself cannot be known for certain.
- Fixed: "The only thing we can know for certain is that nothing else can be known for certain" or, perhaps more sensibly, "Most things may never be known for certain."
- "Nothing you find on a wiki is true."
- This proposition proves too much by invalidating itself, because if true the statement is false, since it appears on a wiki.
- Fixed: "Wikis, like every other source of information, should be evaluated in a critical manner."
- "Human beliefs stem from wish fulfillment, not evaluation of evidence."
- This proposition proves too much by discrediting itself, as it is a human belief, and therefore must be based on wish-fulfillment not evidence.
- Fixed: "Human beliefs stem from any number of sources, one of which is wish fulfillment, not evaluation of evidence."
- "Statements which are not empirically testable are meaningless."
- This proposition (otherwise known as logical positivism), proves too much by invalidating itself, because the statement itself is not empirically testable, and is therefore meaningless by its own criterion.
- Fixed: "Statements that are not axioms and are not empirically testable are meaningless", "Statements which are not empirically testable are generally meaningless." Or maybe "Only philosophic and empirically testable claims are actually meaningful."
- "Nothing outside the Bible is trustworthy."
- This proposition does not actually prove too much, if you can find it in the Bible.
- "There is no objective reality."
- This proposition proves too much by invalidating itself, because the statement tacitly makes an assertion about the objective world (i.e. if you believe there is an objective reality, you're making an objectively false statement).
- Fixed: "The only objective aspect of reality is that it is otherwise subjective."
- ↑ Self-contradiction is one of the simplest fallacies there is.