NASAL AND NASALIZATION
The top of the pharynx is like a crossroads. The airstream can exit the pharynx in either of two ways, depending on the position of the soft palate. If the soft palate is lowered, a portion of the air will pass through the nasal cavity (the remainder finding its way through the oral cavity). If the soft palate is raised, access to the nasal cavity is cut off, and the air can only pass through the oral cavity. The sounds produced via the first method are [+nasal]. Those produced the other way are [-nasal].
Nasality primarily concerns consonants. However, vowels can be nasalized in specific contexts (i.e., when they are followed by nasal consonants). Therefore, the term nasality is used for consonants and nasalization for vowels. Nasalization is fully explained in the following chapters.
[+nasal] phonemes of the vast majority of the world's languages are [+voice]. So, the value [±] for the voicing feature is predictable through a redundancy rule when a phoneme is [+nasal]. Therefore, [+voice] is not included in the bundle of distinctive features of a [+nasal] sound segment.
During the production of these nasal stops, the soft palate is lowered to a greater or lesser extent, allowing a portion of the airstream to pass through the nasal cavity. Occlusion (i.e., air blockage) occurs in the mouth only. Many linguists, therefore, consider [+nasal] phonemes to be stop sounds. However, [+nasal] phonemes can endure through the nasal cavity. In other words, the nasal resonance is continuous. Although a few linguists rank the nasals among the [+continuant] phonemes, the majority of them categorize [+nasal] sounds as [-continuant].
The English language has three [+nasal] sounds in its inventory of phonemes: /m/, /n/, and /ŋ/. Farsi only includes the first two: /m/, and /n/. The phoneme /m/ is a bilabial nasal. The mouth is configured just as for the articulation of the corresponding [-nasal] bilabial stops /p/, and /b/. The lips are pressed tightly together, but the velum is somewhat lowered to let pulmonary air escape through the nasal cavity. The vocal cords are kept close to each other to create audible vibration. The phoneme /n/ is a dental or alveolar nasal. The mouth is configured just as for the corresponding dental or alveolar stops /d/ and /t/. The tongue makes contact either with the front teeth, or with the alveolar ridge directly above them. The phoneme /ŋ/ is a velar nasal. The configuration of the mouth is very close to that of the corresponding velar stops /g/ and /k/. The tongue tip rests against the lower teeth while the back of the tongue makes contact with the soft palate. However, as the soft palate is lowered (to allow air to flow through the nasal cavity), the tongue's back is detached from the soft palate to let a burst of air flow through the mouth.
