The term "tautology" was first introduced by Ludwig Wittgenstein, the Austrian-born British philosopher, who claimed that all necessary suggestions are tautologies as they deliver the same information. The formula of this type of repetition works if it is true under at least one interpretation. The word "tautology" is originated from the Greek word "tautologos" meaning "repeating what has been said", in which "tauto" is "the same" and "logos" is "saying".

Tautology is, in the general understanding, the use of words or phrases that merely repeat parts of the already delivered meaning. "I’d like to apologize because I feel so sorry for losing your keys." Thus, standing in opposition to oxymoron, this tool usually involves two words that not contradict but support each other. 

In grammar, tautology implies an idea that is repeated within the context creating an expression that extra information is provided. "Free gift" seems like a useless repetition, as a gift is free by default. Free is applied, for example, to cause a promotional effect on consumers.

In addition, there are some types of tautological constructions which can be found both in spoken and written language:
●Disjunctions (either x or not x)
●Conditionals (if x then x)
●Equatives (x is x)
●Subordinate sentences (x because x; when x, x)
●Relative sentences (whatever x, x; x, what x)
●Coordinated tautologies (x is x and z is z)

The term tautology was first used in the context of logic by Immanuel Kant in his scientific work “Logic", in which the author described non-explicit arguments as tautological. In propositional logic, this tool is treated as one of the replacement rules. Thus, tautology aims to eliminate redundancy in disjunctions and conjunctions, as they appear to be in logical proofs.

In classic logic, tautology has gained a definition of a universally true statement that takes the value true for all connections of values of its elements. For example, "This athlete will win or will not win." The statement is considered valid if it is truth-preserving, meaning that its structural elements are true, so will be the conclusion.

In rhetoric, tautology is used as an argument that repeats the same statement via different phrases. Oftentimes, the speakers use the unnecessary repetition accidentally without meaning to repeat the idea. In such cases, the speech loses the stylistic sophistication because repetitions sound like a context mistake. 

This rhetoric tool can reduce the power of language by delivering intellectual or creative enrichment when it actually just adds more words or phrases to the context. For this reason, tautology is often defined as a weak rhetorical tool due to the fact that it is more about to distract from the initial statement rather than highlight it.

At the same time, tautology can be applied for the effect to focus attention on the specific idea.
"Alcohol is harmful to your health, and if it is harmful, you can lose several years of your life."
Instead of explaining the harm that can be caused to our health, the author makes the obvious statement by applying the same word meaning one more time.

In literature, tautology is used to highlight key ideas, play with language, and develop musical effect. William Shakespeare in his "Hamlet" refers to this literary device intentionally addressing derision inherent in it.
"What do you read, my lord?"
"Words, words, words."
The repetition is used here to showcase the confusion of the main character as the reaction to Polonius’ words.

As a literary device, tautology is often confused with repetition. However, this literary tool is not the use of the same words and phrases, but the repetition of the same or similar meanings. This literary tool can also be used as an alternative of "analytically true statement". Thus, it is limited to this category that is true according to the formal logical structure of each statement, e.g. "Black is black."

This tool can happen in several forms depending on the sphere of use. The common forms of tautological constructions include:
●Repetitive words and phrases used due to inadequacies in the speech
●Intentional ambiguities
●Poetic technique
●Psychological importance
●Speech by inept speaker or narrator

Tautology can often occur in abbreviations that include the repeated words, such as PIN code, where "PIN" means Postal Index Number. It can also be found across languages, for example, shrimp scampi, where scampi is an Italian equivalent of shrimp.

Despite various uses of tautological constructions in different spheres, there are some universal functions they perform within the context:
●Acceptance or resignation ("But war is war.")
●Denial of differences within a group or a category ("If you’re smart, you’re smart.")
●Providing an extreme example ("Remember when men were men…")
●Distinctness of groups or categories ("Europe is Europe, and America is America.")
●Obligation ("A bet is a bet.")
●Pointing out wysiwyg character ("In the 20th century, a phone was a phone.")

The Summary
Tautology is based on the idea of delivering similar meanings usually via the words different from those of the immediate context. In addition, this term states the idea that is always true considering its syntactical elements. This method has found a wide implementation in logic, grammar, rhetoric, and literature, in which it maintains its standard set of features and functions. Generally, the modern literature tendencies are more oriented on short and to-the-point language instead of using stylistically complex and redundant phrases, such as tautology.