Sound changes involving the lenition of intervocalic consonants are typically restricted to word-internal environments. For instance, in the voicing of intervocalic obstruents in Western Romance, word-internal voiceless plosives were systematically voiced (sapēre > saber), but word-initial segments remained unaffected, so that they remain voiceless even when intervocalic in the phrase (illa porta > la puerta). To give another example, among many that could be found, the change /p/ > /w/ / V__V in 10th century Japanese, as in kapa > kawa ‘river’, is purely word-internal, so that /p-/ fails to undergo the change even in compounds where it is intervocalic, e.g. asa-pi ‘morning sun’ (> asahi as by a later change) (Frellesvig 2010). These sound changes also tend to be regular but may show evidence of lexical diffusion. On the other hand, when we consider synchronic allophonic rules of the same type, it is typically the case that the lenition process applies across the board, without respecting word boundaries:
To try to understand the origins of lexical and word-boundary effects, it may be useful to examine more incipient (“phonetic”) lenitions. Here I will report on a study on the incipient lenition of /ptk/ in Spanish (as well as in Catalan and in Basque), whereby these consonants are voiced and spirantized in postvocalic position. This is a casual speech phenomenon, essentially absent in read speech, but affecting about a third of all intervocalic tokens in conversational speech. We find that word-internal and word-initial consonants after a vowel in the phrase are equally affected by this lenition. Since this is an optional and style-dependent process, it follows that, at least in this case, lenition lacks morpho-syntactic restrictions when it operates as a low-level phonetic process. It also appears to operate on sounds, rather than on specific words.
I will propose a model of sound change where the online variable reduction and overlap of articulatory gestures in casual speech (Browman & Goldstein 1991) is at some point conventionalized as a specific process of phonetic reduction. This conventionalization takes place as the Neogrammarians postulated: phonemes are affected in specific contexts. The conventionalization of the phonetics may later be followed by phonemic recategorization. This recategorization, on the other hand, operates on specific lexical units, not on phonemes. Sound change is phonologically abrupt (even when it appears to be phonetically gradual). There is always phonological discontinuity in sound change (Ohala 1974). Effects such as the restriction to word-internal domains are secondary (Weinrich 1958). Time permitting I will also examine the challenging case of intervocalic lenition in Istanbul Judeo-Spanish.