The importance of phonetics and phonology in english

Many English segments may be articulated in certain contexts as sounds from which they are normally distinguished. [s] is distinguished from [sh] in English, but [s] may be articulated as [sh] in an appropriate context, i. e. when [s] precedes [j], as in this year, or tissue. These distinctions usually go unnoticed within the community if they occur regularly, but can attract attention by those of the non-English speaking community, or those learning English.
The effect of delay on articulator movement can be seen in English words such as more and now, where the beginning of the vowel is nasalized, partly because of the delay in raising the velum at the end of the nasal consonant. The nasality of the initial consonant thus overlaps onto the following oral vowel. A similar effect tends to nasalize the voiced fricative following [n] in such words as burns and bronze.
2) Phonological neutralization is the elimination of a phonemic distinction in a particular phonological context.
With adds and adze, there is a neutralization of the word-final voicing contrast.
In most varieties of English, this occurs in particular before // and (in rhotic dialects) before coda /r/ (that is, /r/ followed by a consonant or at the end of a word); it also occurs, to a lesser extent, before tautosyllabic // and /g/. Some examples of neutralization of // to /e/ before // are beg, egg, Greg, keg, leg, and peg’s coming to rhyme with Craig, Hague, plague, and vague.
Some varieties (including most American English dialects) have significant vocalic neutralization before intervocalic /r/, as well.
Mergers before intervocalic r are quite widespread in North American English.
The mary-marry-merry merger is the mergers of // and // with historical /e/ before intervocalic /r/.
The mirror-nearer merger is the merger of // with /i/ before intervocalic /r/.
The hurry-furry merger is the merger of // before intervocalic /r/ with //.
The furry-ferry merger, common in the Philadelphia accent, is the merger of (//) and (//) before intervocalic /r/.
The tory-torrent merge is the merger of // and // before intervocalic /r/.
The salary-celery merger is a conditioned merger of // and /e/ before /l/ occurring in New Zealand and Victorian English.
The fill-feel merger is a conditioned merger of // and /i/ before /l/ occurring in some dialects of American English.
The fell-fail merger is a conditioned merger of // and /e/ before /l/ occurring in some varieties of Southern American English.
The full-fool merger is a conditioned merger of // and /u/ before /l/ mainly occurring the North Midland accent of American English.
Four other conditioned mergers before /l/ which require more study have been mentioned in the literature and are as follows.
/l/ and /ol/ (bull vs. bowl)
/l/ and /l/ (hull vs. hall)
/l/ and /l/ (bull vs. hull)
/l/ and /ol/ (hull vs. hole)