tautology

Tautology : a statement of the obvious.
"A repetition of the same meaning in different words; needless repetition of an idea in different words" -Webster's
For example:
Adequate Enough or
Ironically-challenged American

In Logic:
An empty or vacuous statement composed of simpler statements in a fashion that makes it logically true whether the simpler statements are factually true or false; for example, the statement

Either it will rain tomorrow or it will not rain tomorrow.

Source: Guru.com

A rule of inference in propositional logic. Written as 'Taut' for short.

P = (P∨P)
And
P = (P∧P)

Basically, 'there is an apple' is the same as 'there is an apple and an apple' and the same as 'there is an apple or an apple'. This is most often used in reverse, so that if you manage to prove (P ∧ P) you can state that you have proved P. Logicians like to be very, very, very precise.

Back up to Rules of Inference
Review your Logic symbols

Tau*tol"o*gy (?), n. [L. tautologia, Gr. : cf. F. tautologie.] Rhet.

A repetition of the same meaning in different words; needless repetition of an idea in different words or phrases; a representation of anything as the cause, condition, or consequence of itself, as in the following lines: --

The dawn is overcast, the morning lowers, And heavily in clouds brings on the day. Addison.

Syn. -- Repetition. -- Tautology, Repetition. There may be frequent repetitions (as in legal instruments) which are warranted either by necessity or convenience; but tautology is always a fault, being a sameness of expression which adds nothing to the sense or the sound.

 

© Webster 1913.