In linguistics, the unnecessary repetition of an idea in different words, e.g. 'a beginner who has just started'.
'My headache hurts' is an example of tautology.
In logic, a statement that is always true by virtue of its logical form, e.g. 'A or not A'. Cross-referenced with 恒真式.
See also: 恒真式
In logic, 'P or not P' is a tautology.