The consonant system of the English language can be studied from phonological, phonetic, phonic, and phonemic viewpoints. An ESL/EFL language teacher would be hard pressed to distinguish among these disciplines of language study. As a matter of fact, so would many linguists, because the concepts are fluid and change with the times. Phonology, for instance, is "the study of sound patterns in languages, sometimes regarded as part of phonetics, sometimes as a separate study included in linguistics. Phonologists study phonemes (vowels and consonants) and prosody (stress, rhythm, and intonation) as subsystems of spoken language" (McArthur, 1992, p. 772). Until the 1960s, phonology's focus was on phonemics--the study of phonemes, viz. phonological units of language "that cannot be analyzed into smaller linear units and that in any particular language is realized in non-contrastive variants" (Oxford English Dictionary, 1989). Since then, phonology's focus has been on sound patterns and prosody. Phonetics is the "study and systematic classification of the sounds made in spoken utterance as they are produced by the organs of speech and as they register on the ear and on instruments" (Webster's Third New International Dictionary, 1966).
From the point of view of the EFL teacher, it is practical to view English consonants as speech sounds which are distinct from vowels, and are individually represented by a letter of the alphabet. Phonologists dichotomize between written consonants and spoken consonants, because the ones may differ from the others in sound. For example, whereas a d is unequivocally an alveolar plosive, such as in dent, a c may sound "hard" (/k/) as in card, candy, and color, and "soft" (/s/) as in city, cent, or Celt. How is a learner of English (L1 or Lx) to know when a c is a /k/ and when it is an /s/? Even native speakers of English often hesitate between the soft /s/ of Glasgow Celtic and the hard /k/ of Celtic language. I...