Lexical diffusion

Dialectologists

Uniform sound change was first challenged by Hugo Schuchardt, a dialectologist of Romance languages, who wrote in his criticism of the Neogrammarians:

Rarely-used words lag behind; very frequently used ones rush ahead. Exceptions to the sound laws are thus formed on both sides.

Dialectologists studying the Romance languages found many apparent exceptions to uniformity, as reflected in their motto, chaque mot a son histoire ('every word has its own history'). This is commonly ascribed to Jules Gilliéron but also originated with Schuchardt.

An example of this phenomenon is the shortening of English 'u' (i.e. the foot-strut split). This sound change results in two different vowels in words such as cut and put. When the isogloss defining this feature in England is examined closely, it emerges that individual words are moving from to over time. It can also be seen that individual speakers fluctuate in their own pronunciation of the same words.

Other arguments against regular, gradual sound change have also been given. For instance, some sound changes, such as metathesis or haplology, are inherently discontinuous and hence incompatible with gradual, imperceptible change.

Wang's reformulation

In 1962, Peking University published Hanyu Fangyin Zihui, containing transcriptions of 2444 morphemes in 17 modern varieties of Chinese. The DOC project at the University of California, Berkeley, headed by William Wang, attempted to apply the comparative method to a computerized form of this data. However, the Chinese data revealed pervasive irregularities.

For example, Middle Chinese words in the third tone class (the "departing" tone) with voiced initials have two forms in the modern Teochew dialect, but no phonetic factor has been found to condition the split. Cheng and Wang list 12 pairs of words that were homophonous in Middle Chinese but have different modern pronunciations. Similar examples were found on other Chinese varieties and other language families. Wang accounted for such irregularities by positing a form of lexical diffusion:

We hold that words change their pronunciations by discrete, perceptible increments (i.e. phonetically abrupt), but severally at a time (i.e. lexically gradual) rather than always in a homogeneous block.

In his view, a sound change would be regular if the change had completed its progress through the lexicon, but irregularity would be seen if the change were still incomplete or if it were interrupted by another change.

Other linguists responded that the explanation of the irregularities should be found in dialect mixture. Indeed, Wang and Lien discovered that the Teochew phenomenon was the result of borrowing from the local literary reading tradition. They present a revised model that distinguishes between the initial "actuation" of a sound change by language contact or internal factors, and its "implementation" by lexical diffusion.

Evaluation

Labov found evidence for both processes, but argued that they operate at different levels:

• Regular sound change occurs when the phonetic realization of a phoneme varies gradually and continuously. The process affects all words containing the phoneme uniformly. Examples include vowel shifts and diphthongization, weakening of glides and unstressed vowels, vocalization of liquids, and changes in the manner of articulation of consonants.
• Lexical diffusion represents a change in the phonemes in a word (substitution, metathesis, elision, epenthesis). It is abrupt and applies to words selected by lexical, grammatical or social criteria.

Paul Kiparsky argues that under a proper definition of analogy as optimization, lexical diffusion is a non-proportional type of analogy similar to leveling, rather than a type of sound change.