In phonology, particularly within historical linguistics, dissimilation is a phenomenon whereby similar consonants or vowels in a word become less similar. Dissimilation is particularly common with liquid consonants such as /r/ and /l/ when they occur in a sequence as demonstrated by these examples in English.
Examples
Dropped initial /r/ in /r..r/ sequence (r-Deletion)
When a sound occurs before another in the middle of a word in rhotic dialects of English, the first tends to drop out, as in "beserk" for berserk, "suprise" for surprise, "paticular" for particular, and "govenor" for governor – this does not affect the pronunciation of government, which has only one, but English government tends to be pronounced "goverment", dropping out the first n. In English, r-deletion occurs when a syllable is unstressed and /r/ may drop out altogether, as in "deteriate" for deteriorate and "tempature" for temperature, a process called haplology. When the is found in, it may change to : "Febyuary" for February, "defibyulator" for defibrillator, though this may be due to analogy with similar words, such as January and calculator.
Dissimilation of /l..l/ to /r..l/
An example where a relatively old case of phonetic dissimilation has been artificially undone in the spelling is English ', whose standard pronunciation is in North-American English, or in RP. It was formerly spelt coronel and is a borrowing from French coronnel, which arose as a result of dissimilation from Italiancolonnell'o''.
There are several hypotheses on the cause of dissimilation. According to John Ohala, listeners are confused by sounds with long-distance acoustic effects. In the case of English, rhoticization spreads across much of the word: in rapid speech, many of the vowels may sound as if they had an r. It may be difficult to tell whether a word has one source of rhoticity or two. When there are two, a listener might wrongly interpret one as an acoustic effect of the other, and so mentally filter it out. This factoring out of coarticulatory effects has been experimentally replicated. For example, Greekpakhu- "thick" derives from an earlier *phakhu-. When test subjects are asked to say the *phakhu- form in casual speech, the aspiration from both consonants pervades both syllables, making the vowels breathy. Listeners hear a single effect, breathy voiced vowels, and attribute it to one rather than both of the consonants, as they assume the breathiness on the other syllable to be a long-distance coarticulatory effect, thus replicating the historical change in the Greek word. If Ohala is correct, one might expect to find dissimilation in other languages with other sounds that frequently cause long-distance effects, such as nasalization and pharyngealization.
Types
Dissimilation, like assimilation, may involve a change in pronunciation relative to a segment that is adjacent to the affected segment or at a distance, and may involve a change relative to a preceding or a following segment. As with assimilation, anticipatory dissimilation is much more common than lag dissimilation, but unlike assimilation, most dissimilation is triggered by non-contiguous segments. Also, while many kinds of assimilation have the character of a sound law, few dissimilations do; most are in the nature of accidents that befall a particular lexical item.
Anticipatory dissimilation
Anticipatory dissimilation at a distance :
Latin *medio-diēs became merīdiēs. Latin venēnum "poison" > Italian veleno. This category includes a rare example of a systematic sound law, the dissimilation of aspirates in Greek and Sanskrit known as Grassmann's Law: *thi-thē-mi "I put" > Greek tí-thē-mi, *phakhu "thick" > Greek pakhus, *sekhō "I have" > *hekhō > Greek ékhō. Some apparent cases are problematic, as in English "eksetera" for etcetera, which may rather be contamination from the numerous forms in eks-, though the common misspellingect. implies dissimilation.
Anticipatory dissimilation from a contiguous segment :
The change from fricative to stop articulation in a sequence of fricatives may belong here: German sechs . In Sanskrit in any original sequence of two sibilants the first became a stop : root vas- "dress", fut. vas-sya- > vatsya-; *wiś-s "clan" > *viťś > *viṭṣ > viṭ ; *wiś-su locative pl. > *viṭṣu > vikṣu. English amphitheater is very commonly pronounced ampitheater. Russian конфорка 'stove burner' is from Dutch komfoor 'brazier'.
Lag dissimilation
Lag dissimilation at a distance :
English "purple" is in medieval English as purpul and purpure and comes from classical Latinpurpura = "purple" with dissimilation of to. Latin rārus "rare" > Italian rado. Cardamom is commonly pronounced cardamon. In Middle English, in some words ending in -n preceded by a coronal consonant the -n changed to -m: seldom, random, venom. English marble is ultimately from Latin marmor. Russian февраль 'February' is from Latin Februārius.
In Spanish, interchanges between and are common; for a list, see History of the Spanish language#Interchange of the liquids /l/ and /r/. In Basque, dissimilation is frequent as well.
Lag dissimilation from a contiguous segment :
Latin hominem > Old Spanish omne > omre > Spanish hombre
In Irish, many dialects regularly change the sequence to
Paradigmatic dissimilation
When, through sound change, elements of a grammatical paradigm start to conflate in a way that is not easily remedied through re-wording, the forms may dissimilate. For example, in modern Korean the vowels and are merging for many people in the capital Seoul, and concurrently the second-person pronoun 네 'you' is shifting to 니 to avoid confusion with the first-person pronoun 내 'me'. Similarly, it appears that English she, historically heo, may have acquired its modern sh form through dissimilation from he, though it is not clear whether the mechanism was idiosyncratic sound change of heo, or substitution of heo with the feminine demonstrative pronounseo.
