We
have seen that nasalisation of vowels in English is non-phonetic because it is
predictable by rule. The vowel nasalisation rule is an assimilation rule; it
assimilates one segment to another by ‘copying’ or ‘sprading’ a feature of a
sequential phoneme, making the two phonemes more similar. Assimilation rules,
for the most part, are caused by articulatory or physiological processes. There
is a tendency when we speak to increase the ease of articulation, that is, to
make it easier to move the articulators. We noted earlier that it is easier to
lower the velum while a vowel is being pronounced before a nasal stop closure
that to wait for the articulators to come together. We can state the vowel
nasalisation rule as :
Nasalise
vowels and dphthongs before nasal (within the same syllable).
This
rules specifies the class of sounds affected by the rule :
Vowels
and diphthongs.
It
is states what phonetic change will occur by applying the rule :
Change
phonemic oral vowels to phonetic nasal vowels.
And
it specifies when the rule applies, the context or phonemic environment.
Before
nasals within the same syllable.
All
three kinds of information segments affected, phonemic environment, phonetic
change must be included in the statement of a phonological rule or it will not
explicitly state the regularities that constitute speakers’ unconscious
phonological knowledge.
Phonologists
often use a shorthand notation to write rules, similar to the way scientists
and mathematicians use symbols. Every physicist knows that E =mc2 means ‘Energy
equals mass times the square of the velocity of light’. Children know that 2 +
2 x 4 / 2 = 8 can be stated in word as ‘two plus two times four divided by two
equals eight’. We can also use such notations to state the nasalisation rule as
:
V
-> [ + nasal ]/ _______ [ + nasal] (C) $
Similar
to the way we use ‘=’ instead of ‘equals’ in mathematical equations and
formulas, we use an arrow ‘->’ instead of ‘becomes’ or ‘is’ or ‘is changed
to’ to represent the change that the rule specifies. The segment on the left of
the arrow is changed to whatever is on the right of the arrow in the specified
environment. The rule applies if the nasal is the final consonant in the
syllable or if it is followed by another consonant as in dam [dæ~m]
and damp [dæ~m]. The optional final consonant is thus put in parentheses, which
means that the segment may or may not be present in the environment.
What occur on the left side of the arrow fulfils the
first requirement for a rule :
It specifies the class of sounds affected by the rule.
What occurs on the right side of the arrow specifies the change that occurs,
thus fulfilling the second requirement of a phonological rule.
To fulfil the third requirement of a rule the
phonological environment or context where the rule will apply we can formalise
the notions of ‘environment’ or ‘in the environment’ and the notion of ‘before’
and ‘after’ since it is also important to specify whether the vowels to be
nasalised occur before or after a nasal. In thi case the [ + nasal] segment in
the context is followed by the syllable boundary symbol $ to show that the rule
only applies if the nasal segment is in the same syllable. In some languages,
nasalisation occurs after rather than before nasal segments. We will use the
following notations :
/ to mean ‘in the environment of’
_____ is placed before or after the relevant
segment(s) that determines the change
The nasalisation rule stated formally can be read in
words :
‘A vowel becomes or is nasalised in the environment
before a nasal segment’.
Any rule written in formal notation can also be stated
in words. The use of the notations is, as stated above, a shorthand way of
presenting the information. It also often reveals the function of the rule more
explicitly. It is easy to see in the formal statement of the rule that this is
an assimilation rule since the change to [ + nasal ] occurs before [ + nasal ] segments.
Assimilation rules in languages reflect what
phoneticians often call coarticulation the spreading of phoneme features either
in anticipation of sounds or the preservation of articulatory processes. This
‘sloppiness’ tendency may become regularised as rule of the language.
The following example illustrates how the English
vowel nasalisation rule applies to the phonemic representation of words and
shows the assimilatory nature of the rule; that is, the [ - nasal ] feature
value of the vowel in the phonetic representation changes to a [ + nasal ] in
the phonetic representation :
There are many other examples of assimilation rules in
English and other languages. There is an optional (‘free variation’) rule in
English that, particularly in fast speech, devoices the nasals and liquids in
words such as snow /snoʊ/ [sn.oʊ] slow /sloʊ/ [sl.oʊ], smart /smart/ [sm.at],
probe /proʊb/ [phr.oʊb] and so on. The feature [ - voiced] of the /s/ or /p/
carries over onto the following segment. Because voiceless nasals and liquids
do not occur phonemically do not contrast with voiced, sonorants the vocal
cords need not react quickly. The devoicing will not change the meaning of the
words; [sl.ɒt] and [slɒt] both mean ‘slot’.
Vowels may also become devoiced or voiceless
environment. In Japanese, vowels (especially high vowels) are devoiced when
preceded and followed by voiceless obstruents; in the words such as sukiyaki
the /u/ becomes [u.] this assimilation rules can be stated as follows :
This rule states that any Japanese vowel (segment that
is non-consonantal and syllabic) become devoiced ([ - voiced]) in the
environment of, or when it occurs between (/), voiceless obstruents. Notice
that the dash does not occur immediately after the slash or at the and of the
rule, but between the segment matrices represented as [ - sonorant, - voiced].
The rule does not specify the class of segments to the
left of the arrow as [+ voiced] because phonemically all vowels in Japanese are
voiced. It therefore simply has to include the change on the right side of the
arrow.
We can illustrate the application of this rule in
Japanese as we did the vowel nasalisation rule in English.
