[1][2] Essentially, in Biblical Hebrew, sometimes the sound /i/ shifted to /a/, but the reason for this development was unclear or debated.
[3] It is "universally supposed to be operative", according to linguists in the field, but criticized as "Philippi's law falls woefully short of what one would expect of a 'law' in historical phonology...."[4] Some critics suggested that it might not even be a rule in Hebrew, but rather a sound rule in Aramaic.
[5] Even Philippi, who mentions it in an article about the numeral '2' in Semitic, proposed that "the rule was Proto-Semitic" in origin.
[6][7] Philippi's law is also used to explain the vowel shift of Proto-Semitic bint for daughter to the Hebrew word bat (בת) and many other words.
[8] This article related to the Hebrew language is a stub.