The current study is aimed at making plausible explanations for phonetic factors that affect the assimilatory phonetic realization in English words. The study reveals that phonetic changes can be traced, and that one of the prime essentials in phonetic changes is lexical stress. Coupled with specific phonemic and graphemic features, lexical stress triggers phonetic changes. The nucleus of a syllable is lengthened, reduced or elided, while the consonant features adjacent to a stressed vowel can be assimilated, dissimilated, epenthesized, voiced, devoiced or elided. With these observations, phonological rules are formulated, which can disclose implicit phonetic features that lead to the assimilatory phonetic realization.