Phonological structure
Phonetic behavior and the resulting acoustic signals are continuous dynamic phenomena. The various phonetic gestures involved in speech production overlap and have no abrupt onsets and offsets. Yet it is generally assumed that phonological structures (phonological forms, phonological representations) underlying speech consist of linear sequences of discrete, static segments. This implies that phonological structures would be structurally similar to strings of alphabetic letters. Such letters are in fact used as phonological notation.
The use of alphabetic writing as the metalanguage of phonology is something which may be assumed to have a significant impact on our theories of phonological structure. Before going on to a discussion of this matter, we should notice, however, that not only the abstract, underlying phonological structure of words is notated by means of discrete graphic symbols. We also use more "concrete" representations of the pronunciations of words and utterances, so-called (narrow) phonetic representations, which are likewise couched in a (modified) letter notation. This means, in all probability, that our view regarding phonetic structure is also influenced by the outer form of this written metalanguage. In any case, it would be utterly naive to believe that phonetic transcriptions, no matter how "narrow" they are, are some kind of mechanically computable, "objective" representations (or reflections) of the phonetic signals. On the contrary, they are the result of a conventional transformation of speech into writing and we need have access to implicit (conventional) rules in order to be able to convert them "back" into speech. It seems probable "that our lack of knowledge of what we are doing when we make phonetic transcriptions is actually hampering our own work as descriptive linguists".
The phonemic principle and the idea of the double articulation of spoken language are probably historically dependent on the existence of alphabetic writing. Thus, if the continuous and varying stream of behavior has to be notated in writing, there arises a need for an economic set of discrete signs, e.g. letters or other symbols (such as pictures). Therefore, a practical notational system presupposes an analysis in terms of segments of some sort. The next step in the argumentation implies that these segmental units are not only workable units of analysis, they are in fact inherent properties of the subject matter; hence phonologists discovered that there were in fact segments underlying overt behavior.
It would be stupid to deny that the idea of underlying segments has some kind of basis in speech production and perception. First of all, the drive towards categorization applies to the perception of speech as well. For this and other reasons patterns and routines are developed also in speech production, the same motor elements tend to be used in the articulation of all words in the language. There insubstantial evidence for units like syllables, syllabic constituents (onsets, nuclei, offsets), vowels and consonants as units of production; common slips of the tongue (such as) 'spictly streaking' for 'strictly speaking', 'strunction and fucture' for 'structure and function', 'lawn drawn' for 'line drawn' are but one type of evidence. Nevertheless, it is no doubt true that writing and the ability to read and write enhance our experience of speech as being composed of segments. What is at stake here is not the general idea that vowels and consonants are components of speech, but rather the much stronger hypothesis inherent in most phonological theories, i.e. that the phonological structure of a word is just a linear sequence of non-overlapping segments. Fowler formulates the basic point of this "strong segment theory" like this:
"Segments in a planned sequence are discrete in the sense that (abstractly stated), their boundaries are straight lines perpendicular to the time axis, so that the terminus of one segment is the beginning of the next segment".
According to mainstream phonological theory, each segment is a bundle of simultaneous features. Such a segment sequence is a basically spatial (rather than temporal) organization of thing-like phonological units arranged in a before-after sequence analogous to the left-right sequences of conventional orthography and conventional phonetic notation. In an extreme version, this theory excludes the possibility that supra-segmental features and syllable structure are phonologically significant.
If the phonologist's view of phonetic structure is influenced by the perspective formed by alphabetic writing, this is true of the layman's thinking about speech to an even greater extent. Aside from the fact that sounds (phonemes) and letters are hopelessly mixed up in the linguistic thinking of most laymen, it is clear that writing distorts our phonetic intuition and make us deaf to certain phonetic realities, notably those which have no counterpart in common orthography.