Redundancy (linguistics)
In linguistics, redundancy refers to information that is expressed more than once. Examples of redundancies include multiple agreement features in morphology, multiple features distinguishing phonemes in phonology, or the use of multiple words to express a single idea in rhetoric. Grammar. Redundancy may occur at any level of grammar. Because of agreement – a requirement in many languages that the form of different words in a phrase or clause correspond with one another – the same semantic information may be expressed several times. In the Spanish phrase "los árboles verdes" ("the green trees"), for example, the article "los", the noun  árboles, and the adjective "verdes" are all inflected to show that the phrase is plural. An English example would be: "that man is a soldier" versus "those men are soldiers." In phonology, a minimal pair is a pair of words or phrases that differs by only one phoneme, the smallest distinctive unit of the sound system. Even so, phonemes may differ on several phonetic features. For example, the English phonemes and in the words "pin" and "bin" feature different voicing, aspiration, and muscular tension. Any one of these features is sufficient to differentiate from in English. Generative grammar uses such  redundancy to simplify the form of grammatical description. Any feature that can be predicted on the basis of other features (such as aspiration on the basis of voicing) need not be indicated in the grammatical rule. Features that are not redundant and therefore must be indicated by rule are called distinctive features. As with agreement in morphology, phonologically conditioned alternation, such as coarticulation and assimilation add redundancy on the phonological level. The redundancy of phonological rules may clarify some vagueness in spoken communication. According to psychologist Steven Pinker, "In the comprehension of speech, the redundancy conferred by phonological rules can  compensate for some of the ambiguity of the sound wave. For example, a speaker may know that "thisrip" must be "this rip" and not "the srip" because in English the initial consonant cluster "sr" is illegal." Rhetoric. Often, redundancies occur in speech unintentionally, but redundant phrases can also be deliberately constructed for emphasis, to reduce the chance that a phrase will be misinterpreted. In rhetoric, the term "redundancy" tends to have a negative connotation and may be perceived as improper because of its use of duplicative or unnecessary wording (and some people expand the definition to include self-contradictory wording , similar to double negation); however, it remains a linguistically valid way of placing emphasis on some expressed idea. Through the use of repetition of certain concepts, redundancy increases the odds of predictability of a message's meaning and understanding to others. Redundancy typically takes the form of tautology: phrases that repeat a meaning with different though semantically similar words. Common examples are: "a variety of different items", "an added bonus", "to over-exaggerate", "and etc.", "end result", "free gift", "future plans", "unconfirmed rumor", "to kill or murder someone to death", "past history", "safe haven", "potential hazard", "completely surrounded", "false pretense , and so on. There is also the self-referential joke organization" called "The Redundancy Society of Redundancy", also called "Society of Redundancy Society". A subset of tautology is RAS syndrome in which one of the words represented by an acronym is then repeated outside the acronym: "ATM machine", "HIV virus", "PIN number", "RIP in peace" and "RAID array". These phases expand to "automated teller machine machine", "human immunodeficiency virus virus", "personal identification number number", "rest in peace in peace" and "redundant array of independent disks array", respectively. "RAS syndrome" is itself a tongue-in-cheek example of the RAS syndrome  in action; it expands to "Redundant Acronym Syndrome syndrome". Another common redundancy is the phrase "i ily you", an 'msn speak' phrase which literally means "i i love you you". A more general classification of redundancy is pleonasm, which can be any unnecessary words (or even word parts). Subsuming both rhetorical tautology and RAS syndrome, it also includes dialectal usage of technically unnecessary parts, as in "off of" vs. "off". Pleonasm can also take the form of purely semantic redundancies that are a part of the de facto standard usage in a language and "transparent" to the user (e.g., the  French question "Qu'est-ce que c'est?" meaning "What's that?" or "What is it?", which translates very literally as "What is it that it is?"). The term pleonasm is most often, however, employed as synonymous with tautology. Redundancy versus repetition. Writing guides, especially for technical writing, usually advise to avoid redundancy, "especially the use of two expressions that mean the same thing. Such repetition works against readability and conciseness." Others make a distinction between redundancy and repetition: Repetition, if used well, can be a good tool to use in your writing. It can add emphasis to what you are trying  to say and strengthen a point. There are many types of useful repetition. Redundancy, on the other hand, cannot be a good thing. Redundancy happens when the repetition of a word or idea does not add anything to the previous usage; it just restates what has already been said, takes up space, and gets in the way without adding meaning. Computer scientist Donald E. Knuth, author of highly acclaimed textbooks, recommends "to state things twice, in complementary ways, especially when giving a definition. This reinforces the reader’s understanding."