designated as regular or not, since they are not complete. However, one can reference the typical characteristics of a change to project whether it will be regular or not. That is, a phonetically gradual change with clear phonetic conditioning falls into Labovs first type, and thus we can project its regularity2.1. American English t/d deletionConsider the deletion of final /t/ and /d/ in American English, which occurs most commonly in words ending in a consonant plus /t/ or /d/, such as just, perfect, child, or grand. This much-studied variable process has been shown to be affected by the preceding and following consonant, with more deletion in a consonant environment; by grammatical status, with less deletion if the /t/ or /d/ is the regular past tense; and by social and age factors, with more deletion among younger, lower socioeconomic class speakers (Labov 1972; Neu 1980).(...) I found that deletion occurred more in high-frequency words. (...)3. Changes that affect low-frequency words firstAs previously mentioned, Hooper (1976) noted a lexical diffusion paradox: sound change seems to affect high-frequency words first, but analogical change affects low-frequency words first. The first tendency has already been documented. The second tendency is evident in the fact that low-frequency verbs, such as weep/wept, leap/leapt, creep/crept, are regularizing, while high-frequency verbs with the same pattern show no such tendency: that is, keep/kept, sleep/slept, leave/left show no evidence of regularizing. Hooper (1976) argued that changes affecting high-frequency words first have their source in the automation of production, whereas changes affecting low-frequency words first are due to imperfect learning. In the latter category are changes that affect words that do not conform to the general patterns of the language. Such exceptional words can be learned and maintained in their exceptional form if they are of high frequency in the input and in general use. However, if their frequency of use is low, they may not be sufficiently available in experience to be acquired and entrenched. Thus they may be subject to changes based on the general patterns of the language.4. Modeling phonetic and lexical gradualnessThe view of lexical diffusion espoused by both Wang and Labov assumes that a change that diffuses gradually through the lexicon must be phonetically abrupt. This is a necessary assumption if one is to accept a synchronic phonological theory that has phonemic underlying representations. Words can change one by one only if the change is a substitution of phonemes in such a theory. The discovery that sound change can be both phonetically gradual and lexically gradual forces a different view of the mental representation of the phonology of words (Hooper 1981; Bybee 2000b). If subphonemic detail or ranges of variation can be associated with particular words, an accurate model of phonological representation must allow phonetic detail in the cognitive representation of words. A recent proposal is that the cognitive representation of a word can be made up of the set of exemplars that have been experienced by the speaker/hearer. Thus all phonetic variants of a word are stored in memory and organized into a cluster: exemplars that are more