It accounts, for example, for the difference between the second vowel of Hebrew שלום (šalom, Tiberian šālōm) and its Arabic cognate سلام (salām).
[1] This vowel shift is well attested in Hebrew and other Canaanite languages, but its exact nature has historically been contested.
He explained the handful of words where *ā shifted to *ō despite *u in the preceding syllable (such as ִרמּוֹן rimmōn ‘pomegranate’ from *rummān-um) as a product of dissimilation of *u to *i when *u was adjacent to a bilabial consonant, a separate sound change which became known as Suchard's Law.
Classical Arabic فاعل (fāʻil) vs. Tiberian Hebrew פועל (pōʻēl)[3] Classical Arabic ات- (-āt) vs. Tiberian Hebrew ות- (-ōṯ) Classical Arabic فعال (fi‘āl, fa‘āl) vs. Tiberian Hebrew פעול (pă‘ōl, pā‘ōl) Classical Arabic فأل (faʼl) vs. Tiberian Hebrew פול, פאל (pōl) In one of the above lexical items (rōš), the shift did not only affect originally long vowels, but also originally short vowels occurring in the vicinity of a historically attested glottal stop in Canaanite.
The shift is especially useful since it affects long vowels whose presence is likely to be recorded by matres lectionis such as aleph and waw, even in a defective consonantal script.