Prove/refute: Every tautology is contingent I'm asking to prove/refute the following statement: > Every tautology is contingent. According to definition of contingent: > _A statement that is neither self-contradictory nor tautological is called a contingent statement. A contingent statement is true for some truth-value assignments to its statement letters and false for others._ Source. Can I tell that the statement is not correct by definition or should I use a more formal way to refute it?

Seeing as "tautology" and "contingent statement" are meta-language definitions (they cannot be expressed in the logical system itself; we're talking _about_ the system) there isn't really a more "formal" way to do it.

You can _expand_ your claim by specifying _why_ a tautology cannot be contingent "by definition", but this won't add to the formality. You can do that if you want practice writing proofs (explaining your conclusions in words) but otherwise I see no added value.