Klingenheben's law describes a series of four historical
sound changes in Hausa which
lenited – in other words, softened – its syllable-final consonants. When the consonant is found in the
syllable onset, the surface and underlying representations of the sound match, but when the underlying consonant is found in
coda, it is converted to its alternative surface form. For example, the
infix , found in some plural words, affects the position of the alternating phoneme within the syllable by shifting the initial syllable's coda consonant to the onset of a new following syllable. In other words, the insertion of
affixes can shift the position of the consonant from the syllable's end to the syllable's beginning, affecting the way that sound is pronounced based on that context, or
alternation.
Velar rule The velar rule affected Hausa's
velar stops – , , and – and probably their
labialized forms – , , and – which became the
semivowel consonant in syllable-final position. A clear example is ('buffalo'), which is derived from an earlier form . There is a syllable boundary between the and the in this earlier form and, since the is a velar stop in syllable-final position, this stop was converted to . In contrast, the plural form contains the long vowel as an infix between and , reorganizing the syllable structure. In this plural form, the is positioned at the start of the syllable and is thus not affected by Klingenheben's law. While the velar rule does occur in word-final position, it is relatively rare.
Coronal rule Similarly, the coronal rule, also referred to as the rhotacization rule, converted the
coronal stops – , , and – to a rolled , written as in the literature. In the
Western Hausa dialect, this rolled resulted in the lateral liquid , probably developing as a later innovation from the rolled . While the rule is thought to have also applied to the coronal
affricate , other sound changes have obfuscated the data; there are no obvious examples of the process having affected it which are not explainable by other processes. The coronal rule is largely responsible for the rhotic distinction between the coronal trill and the
retroflex tap in modern Hausa. Examples of this contrast include the singular ('itinerant trader') with its plural form , which contrasts with the ('beginning') which has a retroflex tap in the same functional environment. The coronal process has remained productive in modern Hausa; terms that exhibit underlyingly syllable-final coronal stops as a result of
clipping demonstrate this
rhotacism. Examples include the unclipped form ('his daughter') with its clipped counterpart . Like the velar process, there are examples of the coronal process occurring in word-final position, such as ('don't!'), though they are few in number. While Klingenheben originally included all
coronal consonants, the evidence conclusively shows that only stops were affected by the process, though certain unexplainable alternations persist. Similarly, there are some examples of word-final alternation with , but these are rare and less commonly used. Klingenheben's analysis also provides for the inclusion of the syllable-final retroflex tap in this rule, but the tap is only replaced with the coronal trill in word-final position, not syllable-final position. Although examples of word-medial, syllable-final shifts from the retroflex tap to the coronal trill are attested, they are the result of other phonological processes. While the coronal fricatives and later assimilated to an adjacent (as evidenced by the lack of these clusters), this is not considered to be a process of Klingenheben's law and is rather a more recent development.
Labial rule Like the velar rule, the labial rule renders the labial obstruents – (from its historical form ), , and – as . The labial process is restricted to the Eastern and Southern dialects of Hausa; it does not affect Western Hausa at all. For example, the Eastern and Southern form ('cotton') differs from its Western counterpart . The labial process is considered incomplete, as it does not have the regular exceptionlessness typically required for a sound law to be considered such.
Paul Newman considers the labial process to be a synchronic snapshot of a diachronic process; that is, the labial rule is a sound law in the process of developing. The change is almost fully completed when the consonant is followed by syllable-initial or . When followed by syllable-initial , , , or , the process is unpredictable and lexically specific. If the following syllable-initial consonant is either , , or , the process rarely occurs at all.
Nasal rule The nasal rule affects the bilabial nasal . It is the only one of the four rules in Klingenheben's law that affects a sound other than an obstruent. Like the labial and the velar rules, it converts the nasal into , though unlike either of the other rules, it requires that the following syllable-initial consonant be a coronal
sonorant. The rule does not apply unless the occurs before a syllable-initial or . The nasal process, like the labial process, is limited to particular dialects. In non-Western dialects, the will simply
assimilate to the following consonant's
point of articulation. Contrast the Western Hausa term ('morning star') with the dialectal variant rather than . The nominal derivational suffix , used for expressive depictions of sounds and actions, appears to block the nasal process altogether, as seen in the contrast between ('moving around in ragged clothes'), which affects the preceding velar, and ('speaking unintelligibly'), where the and meet at the syllable boundary. Because of the distinct subsystem of behavior ideophones exhibited in Hausa, the effect of the suffix is considered to be a morphological exception rather than a phonological one; that is, ideophones form a separate class of words which are not subject to the same phonological constraints as other classes.
Effect on vowels The process sometimes affected the preceding vowels. In syllables where the final consonant is a velar and the preceding vowel was either or , the resulting vowel was the long vowel . This change explains the relationship between words like ('body'), which were not affected by the law, with those like ('one another'), which were affected. In this example, the historical form had its velar consonant affected by labializing process, becoming . The resulting sequence was reinterpreted with the long vowel .
Blocking Klingenheben's law has been used to describe possible explanations for
geminate inalterability, a process wherein phonological rules affecting a short single phoneme – known as a "singleton segment" – are
blocked in comparable positions when the phoneme is geminated. Hausa syllable structure does not allow for
tautosyllabic consonant clusters and thus these geminates can be understood as heterosyllabic; that is, the geminate straddles both sides of the syllable boundary. Any syllable-final consonant which as a singleton would be converted to a sonorant in accordance with Klingenheben's law is not converted in this syllable-final position if it is a geminate. ==Relative chronology==