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Programmer here. I sometimes catch myself saying that something is a Tautology False because it always evaluates to FALSE or OFF. I know Tautology means always True in discrete math but I use it to describe something that doesn't change. It's always constant in being False or Null, etc. Am I being illogical.

christian winterhalter
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    I'm not sure "tautology false" is even grammatically correct. If you rephrase it to "tautologically false", then we can debate whether that is proper usage. – Misha Lavrov Nov 09 '23 at 19:51
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    Just say "always". – Ethan Bolker Nov 09 '23 at 19:58
  • Some phrases you might see used in logic for something that is always false are "contradictory/a contradiction", "impossible/an impossibility", "absurd/an absurdity", "invalid/an invalidity". Just saying "it's always false" is fine too. You could say "its negation is a tautology" or "it's the negation of a tautology". "Tautologically false" sounds a bit weird to me. Beware the meaning of "tautology" in logic is subtle. EG "for all $n \in \Bbb N$, $n$ is of the form $2k$ or $n$ is of the form $2k + 1$" would be a theorem rather than a tautology. – Izaak van Dongen Nov 10 '23 at 03:02
  • In logic, we say Contradiction a proposition that is always FALSE. Obviously, being a tautology a proposition that is always TRUE, the negation of a tautology is a contradiction. – Mauro ALLEGRANZA Nov 10 '23 at 08:05

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