Philippi's law

[Aleppan]

I read this

Philippi’s Law is a sound rule, articulated by the Semitist, F. W. M. Philippi, in a lengthy article on the form of the numeral ‘two’ (Philippi 1878), according to which Proto-Semitic short *i became *a in originally closed, stressed syllables. Philippi cited possible instances in Aramaic and Ethiopic, as well as Hebrew, and so proposed that the rule was Proto-Semitic (PS). The Ethiopic, and perhaps the Aramaic, examples may be explained in other ways, but ‘Philippi’s Law’ was accepted as valid for Hebrew by several noted scholars (that's all you get without having access)

So, why do we say כְּבַדְתֶּם instead of כְּבִדְתֶּם? The syllable of i is not stressed!

 

[Drink]

The exact criteria for this law are not well understood.

It could be that it was extended due to morphological leveling.

Or it could be that it applied in unstressed syllables as well in some cases.

 

[Ali Smith]

What about in the construct form of בַּת? Why does Philippi's law apply there? It doesn't apply in בִּתִּי 'my daughter'.

And why does it not apply to תֵּת, the infinitive construct of נָתַן? I mean, it applies to רֶדֶת and שֶׁבֶת, the infinitive constructs of יָרַד and יָשַׁב, respectively, doesn't it? Shouldn't the infinitive construct of נָתַן have been תֶּנֶת in accordance with Phillipi's law?

 

[Drink]

As I said, the exact criteria for this law are not well understood.

It may be better to call it a trend, rather than a law.

 

[radagasty]

Philippi’s Law leaves much to be desired as a phonological law, and, in all likelihood, it would seem to me, represents a loose collection of disparate but similar sound changes that operated at different periods in the history of the Hebrew language.

 

[Ali Smith]

Why didn’t it apply to the second syllable כָּבֵד “it was heavy”?

 

[radagasty]

As I suggested, the term Philippi’s Law is often used as an umbrella term for disparate (albeit similar) sound changes operating at different times, but, restricting its definition to that given in the OP, viz. that “Proto-Semitic short *i became *a in originally closed, stressed syllables”, then the second syllable of כָּבֵד was not originally closed, and quite possibly not stressed either.