Some of sequential constarains on phonemes that were discussed previously may show up as phonological and morphophonemic rules. The English homorganic nasal constraint applies between some morphemes as well as within a morpheme. The negative prefix in-, which (like un-) means ‘not’, has three allomorphs which respond to this constraint :
The
pronunciation of this moepheme is often revealed by the spelling as im- when it
is prefixed to morphemes beginning with /p/ or /b/. Because we have no letter ‘ŋ’
in our alphabet (although it exists in alphabets used in other languages), the
velar [ŋ] is written as n in words such as incomplete. You may not realise that
you pronounce the n in inconceivable, inglorious, incongruous, and other such
word as [ŋ] because your homorganic nasal rule is as unconscious, and other
rules in your grammar. It is the job of linguists and phoneticians to bring
such rules to consciousness or to reveal them as part of the grammar. If you
say these words in normal tempo without pausing after the in-, you should feel
the back of your tongue rise to touch the velum.
In Akan the negative morpheme also has three nasal
allomorphs: [m] before /p/, [n] before /t/, and [ŋ] before /k/, as is shown in
the following cases :
We see, then, that one morpheme may have different
phonetic forms or allomorphs. We have also seen that one morpheme may occur in
the language with the same meaning but different forms in-,un-, and not (all
meaning ‘not’). It is not possible to predict which of these forms will occur,
so they are separate synonymous morphemes. It is only when the phonetic form is
predictable by general rule that we find different phonetic forms of a single
morpheme.
The nasal homorganic rule is a feature-changing rule.
It can be stated simply as :
Change the place of articulation of a nasal consonant
so that it agrees with the place feature value of a following consonant.
In other words, nasal consonants agree in place of
articulation with a following consonant.
Given this rule, we can represent this in- negative
prefix morpheme by the phoneme representation /ɪn/. Before vowels and before
morphemes beginning with /t/ or /d/, the homorganic nasal rule will change
nothing since the rule is not violated. The morpheme will be represented by the
allomorph [ɪ~n] (after the vowel nasalisation rule applies) as, for example, in
the words indecision, interminable, inoperative. Before a morpheme beginning
with a labial consonant /b/ or /p/, the alveolar feature of /n/ will be changed
by the rule to agree with the place of articulation of the labials, as in
impossible and impertinent. Similarly, this feature-changing rule will
assimilate the /n/ in /ɪn-/ to a velar nasal before morphemes beginning with
/k/ or /g/ in words such as incoherent.
Deriving all forms of the morpheme from /ɪn-/ is the
simplest way of revealing this mophological/phonological knowledge. One could
represent the morpheme as /ɪm-/ or /ɪŋ-/ instead. But the rule would then have
to be complicated.
Change the pace of articulation of a nasal consonant
so that it agrees with the place feature value of a following consonant and
change the nasal consonant to [n] before a vowel.
This will derive the correct forms of the morpheme but
in a more complex fashion than is needed. Rule statements should be as simple
and elegant as possible. This principle, known as Occam’s Razor, applies not
just in phonology but in all of science. In essence, the simpler the rule, the
more general the explanation.
Thus, when two allophones can be derived from one
phoneme, one selects as the underlaying segment the allophone that makes the
rules and the phonemic feature matrices as simple as possible. For example,
deriving the unaspirated and aspirated voiceless labial stops in English from
an underlaying /p/ makes aspiration redundant and unnecessary as a phonemic
feature value. If /ph/ were the phoneme, the phonemic features would be more
complex.
In some cases, different phonetic forms of the same
morpheme may be derived by segment-deletion rules, as in following examples :
In none of the words in column A is there a phonemic
[g], but in each corresponding word in column B a [g] occurs. Our knowledge of
English phonology accounts for these phonetic differences. The ‘[g]-no[g]’
alternation is regular, and we apply it to words that we never have heard
before. Suppose someone says :
‘He was a salignant [səlɪgnə~nt] man.’
Even if you do not know what the word means, you migh
ask (perhaps to hide your ignorance):
‘Why, did he salign [səlãɪn]
somebody ?’
It is highly doubtful that a speaker of English would
pronounce the verb from with the –ant dropped as [səlɪgn], because the
phonological rules of English would ‘delete’ the /g/ when it occured in this
context. This rule migh be stated as :
Delete a /g/ when it occurs before a final nasal
consonant.
The
rule is even more general, as shown by the pair gnostic [nɒstɪk] and agnostic [ægnɒstɪk]
and the word cognition, recognition, agnosia, and others, all of which contain
the same morpheme related to knowledge. It can be stated as :
Delete
a /g/ when it occurs word initially before a nasal consonant or before a
word-final nasal.
Given
this rule, the phonemic representation of the stems in sign/signature,
design/designation, resign/resignation diaphragm/diaphragmatic will include a
phonemic /g/ that will be deleted by the regular rule if a suffix is not added.
By stating the class of sounds that follow the /g/ (nasal consonants) rather
than any specific nasal consonant, the rule deletes the /g/ before both /m/ and
/n/.
An
alternative analysis is to represent the root morpheme sign as /saɪn/. No /g/
would have to be deleted to derive the verb, but to derive the noun signature
an insertion rule would be required and all the words that have a [g] in the
derived words an no [g] in the roots would have to be listed. By representing
the root morphemes with a phonemic /g/, the regular, automatic, non-excepyional
rule of /g/ delection stated above derives the correct forms and also reveals
this phonotatic constraint in the language.
The
phonological rules that delete whole segments, add segments and features, and
change features also account for the various phonetic forms of some morphemes.
This point can be further illustrated by the following words :
A
speaker of English knows when to pronounce a final /b/ and when not to. The
relationship between pronunciation of the A words and their B counterparts is
regular and can be accounted for by the following rule :
Delete
a word-final /b/ when it occur after an /m/.
Notice
that the underlying phonemic representation of the A and B stems is the same.
The
rules that delete the segments discussed above are general phonological rules,
but their application to phonemic representations results in deriving different
phonetic forms of the same morpheme.
