Unchangeable vowels in Biblical Hebrew are those that resist reduction, modification, or lengthening due to their inherent phonological or morphological properties. These include vowels that are long by nature or contraction—such as î, ê, û, and ô—often marked with vowel letters (e.g., ִי, ֵי, וּ, וֹ) and typically stable across forms, even when spelled defectively. The naturally long â (impure Qameṣ) also belongs to this category, though it is rarely marked with a consonant and must be distinguished from tone-induced length through morphological analysis. Short vowels in closed, non-final syllables, or those preceding Dageš forte in sharpened syllables, are likewise generally unchangeable. Additionally, long vowels that arise in open syllables due to the inability to double a following guttural or ר (e.g., מֵאֵן, בֹּרַךְ) are considered stable. While early grammarians sometimes viewed these vowels as abbreviated forms of fuller spellings, their resistance to change is grounded in consistent phonological behavior and grammatical structure.
a. Unchangeable vowels in Hebrew—those not subject to attenuation (i.e., reduction to Šewâ), modification, lengthening, or shortening—can only be identified with certainty by examining grammatical forms. Occasionally, comparative Semitic evidence (especially Arabic; see § 1 m) provides further clarity. This principle applies particularly to vowels that are long by nature or contraction, as opposed to vowels that are only rhythmically long (due to stress or syllabic structure). These rhythmically long vowels are more susceptible to becoming short again or collapsing into Šewâ when the stress shifts or syllables are rearranged.
b.1. The vowels of the second and third classes—î, ê, û, ô—are essentially long and, as a rule, unchangeable (cf. § 26 p, § 27 n–o). These can often be recognized by their accompanying vowel letters: ־ִי, ־ֵי, וּ, וֹ. Examples include:
- יֵיטִיב “he does well”
- חֵיכָל “palace”
- גְּבוּל “boundary”
- קוֹל “voice”
Despite frequent defective spelling (see § 8 i)—such as יֵטִיב or קֹל—this is merely an orthographic choice and does not alter vowel length. For example, גְּבֻל still contains a long û just as in גְּבוּל.
In some cases, a vowel that is only long due to tone may also be written fully (with a mater lectionis), as in יִקְטוֹל instead of יִקְטֹל.
c.2. The essentially or naturally long â (known as impure Qameṣ; cf. § 9 q) generally lacks a consonantal marker in Hebrew, unlike in Arabic where it is typically represented by א. Only in rare cases (cf. § 9 b; § 23 g) does Hebrew indicate this vowel with a consonant. Distinguishing between this naturally long â and a tone-long ā requires a firm understanding of morphological forms.
d.3. Short vowels in closed, non-final syllables (§ 26 b) are usually unchangeable. Examples include:
- מַלְבּוּשׁ “garment”
- מִדְבָּר “wilderness”
- מַמְלָכָה “kingdom”
Likewise, short vowels that appear before Dageš forte in sharpened syllables tend to be stable, e.g., גַּנָּב “thief.”
e.4. Long vowels resulting from the absence of consonant doubling—especially when a guttural or ר prevents strengthening—are unchangeable when they occur in open syllables. For instance:
- מֵאֵן instead of mĭʾʾēn
- בֹּרַךְ instead of burrakh
Note: Early Hebrew grammarians referred to vowels that are regularly followed by vowel letters as vocales impurae. Thus, a form like כְּתָב (kethâbh) was seen as an abbreviated spelling for כְּתָאב, and similar cases.
