
Logic ◾ 77
to be a contradiction. Since a tautology is always True, a tautology can be
understood as simply a long-winded way of expressing something that is
self-evident. Of course, a contradiction can be understood as a statement
that is always logically invalid no matter how you look at it. Tautologies
and contradictions should be avoided when writing propositions and they
should also be avoided in the normal course of human conversations since
such statements do not express any sort of productive line of reasoning. e
following propositions give examples of a tautology and a contradiction.
Tautology: P or not P
Contradiction: P a