Horror aequi

Horror aequi,^[a] or avoidance of identity,^[2]^: 100 is a linguistic principle that language users have psychological^[3]^: 266 or physiological^[1]^: 51 motives or limits on cognitive planning^[1]^: 51 to avoid repetition of identical linguistic structures.

The term originated in 1909 in Karl Brugmann,^[4]^: 219 who used it to explain dissimilation,^[3]^: 266 the tendency for similar consonants or vowels in a word to become less similar,^[5]^: 146 which can often be chalked up to simply "euphony".^[4]^: 219 Today, however, the term is usually applied instead to grammatical elements or structures.^[4]^: 219

One of the most widely cited definitions^[6]^: 39^[7]^: 71 is that of Günter Rohdenburg: "the horror aequi principle involves the widespread (and presumably universal) tendency to avoid the use of formally (near-)identical and (near-)adjacent (non-coordinate) grammatical elements or structures."^[8]^: 205

In the study of phonology, such avoidance falls under the obligatory contour principle,^[2]^: 100 which holds that certain consecutive identical sounds are not permitted^[9]^[10]^: 383–84 (such as in Mandarin Chinese, where two third tones are not used consecutively^[11]^: 104).

The term horror aequi is sometimes extended to the stylistic preference to avoid repeating the same word in a given text.^[12]

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