How does the vav ha-hipuch change the vowels of verbs?

Question

I'm trying to understand why the 3rd person masculine singular imperfect of אמר conjugated under the pa'al binyan has a vowel change from patach to segol under the mem: no vav prefix: יֹאמַר vav prefix: וַיֹּאמֶר in Shemot 6:2: > וַיֹּאמֶר אֵלָיו אֲנִי ה in Job 39:25: > בְּדֵי שֹׁפָר יֹאמַר הֶאָח I'm assuming this change is similar to other regular vowel changes that occur in Hebrew like the patach under the definite article ה changing when put before certain letters. Otherwise we'd have to memorize all the special forms of verbs after prefixes... If someone could reference a grammatical work which discusses this vowel change rule I would appreciate it.

Answer 1

This is an excellent, high-level question. The vowel change between יאֹמַר and וַַיּאֹמֶר is due to a shift in stress. In יאֹמַר the stress is at the end of the word, hence the long patach, but when we lengthen it to וַַיּאֹמֶר the stress is moved up a syllable. This shift causes vowel reduction. What makes this particular case unique is the guttural-like ר at the end of the word. This letter prefers a segol for vowel reduction, hence verbs like וַיָצֶר and nouns like בֹּקֶר. So, when a ר is involved the reduced vowel becomes a segol.

For the two principles I mentioned see "A Grammar of Biblical Hebrew" (Jouon-Muraoka) §23b and §73d-e.