The so-called segholates developed from mono-syllabic nouns ending with a consonant cluster that resulted from the loss of final short vowels sometime during the late second millennium in common NWS. Interestingly, Hebrew and Aramaic form segholates differently. The Hebrew pattern is qVtVl (with stress on the first syllable) while the Aramaic pattern is qətVl (with stress on the final syllable). For instance:
*káspu > Heb kέsεf but BA kəsáf
*sípru > Heb séfer but BA səfár
*rúgzu > Heb róγεz but BA rəgáz
Malone suggests that the different patterns may be explained by differences in sequencing, namely the order of epenthesis and stress shift in the two languages.
It should be noted that there are also some deviations to these patterns in individual words. For instance, *šákmu ‘shoulder’ > Heb šəkέm, and *hílmu ‘dream’ > BA hélεm. Further, in Hebrew the pattern qətVl seems to dominate in nouns II-ˀ and III-y such as *diˀbu ‘wolf’ > zəˀév and *gadyu ‘kid’ > gəḏí.
Based on comparative evidence and internal reconstruction, the following stages may be reconstructed for Hebrew segholate formation:
a) Final short vowels are apocopated.
b) Stress shifts to the final syllable.
c) Final consonant clusters are broken by an epenthetic vowel (usually e, but a if preceding consonant is a guttural).
d) Post-vocalic non-geminate non-pharyngealized consonants are spirantized (ie bgdkpt letters).
f) Unstressed e lowers to ε.
g) Stressed vowels undergo certain changes in quality: á umlauts to έ when separated by one consonant from following ε (á > έ /_xCε) while í and ú lower to é and ó respectively.
h) Closed-syllable ε lowers and backs to a when immediately followed by a guttural.
Following are some examples:
*sípru > sípr (a) > síper (c) > sífer (d) > sífεr (f) > séfεr (g)
*báˤlu > báˤl (a) > báˤal (c)
*pátḥu > pátḥ (a) > páteḥ (c) > páθeḥ (d) > páθεḥ (f) > pέθεḥ (g) > pέθaḥ (h)
Biblical Aramaic, however, follows a different sequence:
a) Final vowels apocopated.
b) Final consonant clusters broken by epenthesis (usually e, but o when following vowel is u).
c) Stress shifts to final syllable.
d) Spirantization of post-vocalic bgdkpt.
e) Open-syllable short vowels reduced to ə in pretonic position.
f) a lowers and backs to ă when preceded by a guttural.
h) Segholate é lowers and backs to á when a guttural or r immediately follows.
*gábru ‘man’ > gábr (a) > gáber (b) > gabér (c) > gavér (d) > gəvér (e) > gəvár (h)
*qúšṭu ‘truth’ > qúšṭ (a) > qúšoṭ (b) > qušóṭ (c) > qəšóṭ (e)
Comparison with other Aramaic dialects suggests that changes a-e belong to the Common Aramaic phase of the language. For instance, in Jewish Palestinian Aramaic (JPA) the changes are similar to Biblical Aramaic except that stage h is modified:
j) Segholate é is replaced by á, unless a guttural immediately precedes. Segholate ó tends to be replaced by á.
*rúgzu > rúgz (a) > rúgoz (b) > rugóz (c) > ruγóz (d) > rəγóz (e) > rəγáz (j)
In Christian Palestinian Aramaic (CPA) there is no evidence of the vowel changes in steps f, g, or h. In Syriac, different vowel changes occur in stages f and h:
f) In word-initial ˀə the ə is replaced by u when the following vowel is u, otherwise it is replaced by e or a. Further, word-initial yə > ī.
h) Segholate é or ó lower to á when followed by a guttural or r.
*yárḥu > yárḥ (a) > yáreḥ (b) > yaréḥ (c) > yəréḥ (e) > īréḥ (f) > īráḥ (h)
Mandaic follows the same stages as Syriac a-f, shares Biblical Aramaic stage h, and then has several peculiarly Mandaic developments.
When we compare Hebrew stages a-h with Aramaic, it is evident that they are very similar. Stages a and d are identical, while Hebrew stage b is identical to Aramaic stage c and vice-versa. Thus the difference between the two is the order of epenthesis and stress-shift. It seems likely that both languages are sharing in the same process of sound change, otherwise it is difficult to explain how the same changes could have occurred independently in the two languages. But how could stages b and c be reversed in the two languages?
It seems impossible if we conceive of each change as an instantaneous event, but not if it is conceived as a process through time. The common Northwest Semitic speech community was relatively unified for a time, but overlapping pre-Aramaic and pre-Hebrew groups may have begun to form. The apocopation of final vowels seems to be a common change to all dialects, but if stress shift began in the pre-Hebrew area (probably centering in the South) and epenthesis in the pre-Aramaic area (probably centering in the North), then by the time stress-shift reaches Aramaic, epenthesis will already have occurred, and by the time epenthesis reaches Hebrew, stress-shift will already have occurred.
Thus we have an example of the wave theory of language change. This theory also helps explain the deviations noted at the beginning. The Hebrew qətVl forms can be explained as forms in which epenthesis preceded the stress shift. These forms then follow a process augmented by the Aramaic stages e-h, along with Hebrew stage g. For instance:
*gábru > gábr (a) > gáber (c) > gabér (b) > gavér (d) > gəvér (e) > gəvár (h)
Similarly, the Biblical Aramaic qVtVl forms can be explained as forms in which stress shift has preceded epenthesis. These forms then follow a process augmented by the Hebrew stages f and g . For instance:
*ṣálmu > ṣálm (a) > ṣálm (c) > ṣálem (b) > ṣálεm (f) > ṣέlεm (g)
With such a wave model, it is not unexpected that these features would reach peripheral dialects at different times, if at all. Thus it is interesting to note that many of Hebrew qətVl forms seem to have a rural provenance: dəváš ‘honey’, səváḥ ‘thicket’, šəlɔẃ ‘quail’, etc.
Finally, the II-ˀ and III-y forms can also be explained by a switch in the order of epenthesis and stress shift. Linguistic change often originates sporadically, becomes conditionally regular, and then unconditionally regular. These special forms may represent the first phases of the process, when only some word final clusters (namely ˀC and Cy) were subject to epenthesis. At this point, stress shift had not yet become regular. In addition, the nature of the epenthetic vowel seems to have differed from the later stage.