In phonology, particularly within historical linguistics, dissimilation is a phenomenon whereby similar consonants or vowels in a word become less similar. In English, dissimilation is particularly common with liquid consonants such as /r/ and /l/ when they occur in a sequence. 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 "" for berserk, "" for surprise, "" for particular, and "" for governor – this does not affect the pronunciation of government, which has only one , but English government tends to be pronounced "", dropping out the first n. In English, r-deletion occurs when a syllable is unstressed and may drop out altogether, as in "" for deteriorate and "" for temperature, a process called haplology. When the is found in , it may change to . (, → February, which has been explained by phonotactic factors or alternatively by morphological analogy with more common sequences such as January. nucular, which may have arisen through an analogous process) 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 colonel, whose standard pronunciation is (with the r sound) 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 Italian colonnello. Dissimilation of /r..r/ to /l..r/ Latin peregrinus > Old French pelegrin (and the Italian pellegrino and Sicilian piḍḍigrinu) which gave rise to the English . Causes 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, Greek pakhu- (παχυ-) "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