When two sound segments occur in sequence and some aspect of one segment is taken or “copied” by the other, the process is known as assimilation. If we think of the physical production of speech, we realize that this regular process happens simply because it’s quicker, easier and more efficient for our articulators as they do their job. Think of the word have /hæv/ by itself, then think of how it is pronounced in the phrase I have to go in everyday speech. In this phrase, as we start to say the /t/ sound in to, which is voiceless, we tend to produce a voiceless version of the preceding sound, resulting in what sounds more like /f/ than /v/. So, we typically say [hæftə] in this phrase and you may even see it written informally as “hafta,” showing how the assimilation from a voiced to a voiceless sound is perceived.

Vowels are also subject to assimilation. In isolation, we would typically pronounce [ɪ] and [æ] without any nasal quality at all. However, when we say words like pin and pan in everyday speech, the anticipation of forming the final nasal consonant will make it easier to go into the nasalized articulation in advance and consequently the vowel sounds in these words will be, in more precise transcription, [ı˜] and [æ˜ ] This is a very regular feature of English speakers’ pronunciation. It is so regular, in fact, that a phonological rule can be stated in the following way: “Any vowel becomes nasal whenever it immediately precedes a nasal.”

This type of assimilation process occurs in a variety of different contexts. By itself, the word can may be pronounced as [kæn], but, when we say I can go, the influence of the following velar [ɡ] will almost certainly make the preceding nasal sound come out as [ŋ] (the velar nasal) rather than [n] (the alveolar nasal). The most commonly observed conversational version of the phrase is [aɪkəŋɡoʊ]. Notice that the vowel in can has also changed to schwa [ə] from the isolated-word version [æ]. In many words spoken carefully, the vowel receives stress, but in the course of ordinary everyday talk, that vowel may no longer receive any stress and naturally reduce to schwa. We may, for example, pronounce and as [ænd] by itself, but in the normal use of the phrase you and me, we usually say [ən], as in [juənmi].