Final answer:
Individual phonemes vary in pronunciation due to allophones, influencing the changes in sounds depending on adjacent speech sounds. This phonological variation is evident in regional dialect differences and is integral to the study of language and speech.
Step-by-step explanation:
Individual phonemes are pronounced somewhat differently depending on the speech sounds before and after them because of allophones. This concept is central to understanding variations in pronunciation and is closely related to the study of dialects and linguistic shifts in language. For instance, variations in pronunciation, such as the way vowels before [r] are often pronounced distinctly from vowels before other consonant sounds, underscore the influence of surrounding sounds on phoneme articulation. This is observable in regional dialects where, for example, the simple word 'wash' becomes 'warsh,' or in grammatical constructions where an additional /s/ may be added as in 'Alls we need is more ice cream.' Such phonological variation reflects the dynamic nature of language as it adapts to geographical, cultural, and social influences.