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Tautology (from Greek tauto, "the same" and logos, "word/idea") is an unnecessary repetition of meaning, using dissimilar words that effectively say the same thing (often originally from different languages). It is considered a fault of style and was defined by A Dictionary of Modern English Usage (Fowler) as "saying the same thing twice," if it is not apparently necessary for the entire meaning of a phrase to be repeated. An example of a tautology is the phrasing "close proximity". If a part of the meaning is repeated in such a way that it appears as unintentional, or clumsy, then it may be described as tautology. On the other hand, a repetition of meaning which improves the style of a piece of speech or writing is not necessarily described as tautology. In evaluating world views, logicians do not concern themselves that the premises are correct or not, but whether the conclusions derive logically.
A rhetorical tautology is defined as a series of statements that form an argument, whereby the statements are constructed in such a way that the truth of the proposition is guaranteed or that, by defining a dissimilar or synonymous term in terms of another, the truth of the proposition or explanation cannot be disputed. Consequently, the statement conveys no useful information regardless of its length or complexity making it unfalsifiable. It is a way of formulating a description such that it masquerades as an explanation when the real reason for the phenomena cannot be independently derived. A rhetorical tautology should not be confused with a tautology in propositional logic, which by the precepts of empiricism is not falsifiable.
Rhetorical tautologies state the same thing twice, while appearing to state two or more different things, while logical tautologies state the same thing twice and must do so by logical necessity. The inherent meanings and subsequent conclusions in rhetorical and logical tautologies or logical necessities are very different. Logical tautologies are neither refutable nor verifiable under any condition by axiomatic necessity.
Rhetorical tautologies guarantee the truth of the proposition, where the expectation (premise) was for a testable construct, any conclusion is by the precepts of falsificationism a non sequitur (logic). Circular reasoning differs from tautologies in that the premise is restated as the conclusion in an argument, instead of deriving the conclusion from the premise with arguments, while tautologies states the same thing twice. If the argument that separates the conclusion from the premise is a logical fallacy such as a rhetorical tautology, then the premise is merely restated as the conclusion and did not derive in a logical fashion from the premise. The form the arguments are allowed to take, either falsifiable or unfalsifiable(logical validities) dictates in what way the conclusion can logically derive from the premise, without merely restating the premise. Aristotle's "begging the question", "begging the premise" or "requesting the premise" means a conclusion is stated without specifying the premise which is not the same concept as a circular argument. Without knowledge of the premise it is not possible to determine if the conclusion derives logically from the premise. To "raise the question" or to "raise the conclusion" means a specified premise raises a question or a series of questions that will determine in what way any conclusion derives logically from the premise. In both the phrases "raising the question" and "begging the question" the same term 'question' is used as a dissimilar reference to premise and conclusion respectively. The phrases derive their meaning by reflectivity to each other in the same way that light is understood as the semantic opposite of darkness. Because the same term - 'question' - is used as a dissimilar reference to two dichotomous concepts it leads to them being confused with one another.
Intentional repetition of meaning 
Intentional repetition of meaning intends to amplify or emphasize a particular thing about what is being discussed: to repeat it because one cares about it. A gift is by definition free of charge, but one might talk about a "free gift" to emphasize that there is no fine print, be it money or an expectation of a return, or that the gift is being given by volition.
This is related to the rhetorical device of hendiadys, where one concept is expressed through the use of two, for example "goblets and gold" meaning wealth, or "this day and age" to mean the present time. Superficially these expressions may seem tautologous, but they are stylistically sound because the repeated meaning is just a stylized way to emphasise the same idea.
Much Old Testament poetry is based on parallelism: the same thing said twice, but in slightly different ways (Fowler puts it as pleonasm). This can be found frequently in the Psalms, the Books of the Prophets, and in other areas of the Bible as well. One explanation of this is that when the Bible was translated into Anglo-Saxon, Norman French was still common among the aristocracy, so expressions like "save and except" were translated both for the commoners and the aristocrats; although in this case both "save" and "except" have a French or Latin origin.
Fowler makes a similar case for double negatives; in Old English they intensified the expression, did not negate it back to being a positive, and there are plenty of examples in authors before the eighteenth century, such as Shakespeare. In Modern French, for example, the "ne-pas" formation is essentially a double negative, and in many other Western European latinate languages the same applies, with "ni" or "no", mutatis mutandis, emphasising instead of negating the initial negative. In common French, the "ne" is quite typically dropped, as it was believed to have been in Vulgar Latin.
See also 
|Look up tautology in Wiktionary, the free dictionary.|