verbs ל״ה, e.g. originally גָּלַי=גָּלַ(י)=גָּלָה, since ă after the rejection of the י stands in an open syllable, and consequently must be lengthened to ā. The ה is simply an orthographic sign of the long vowel. So also שָׁלָה for šālaw.  On the origin of יִגְלֶה, see §75e; on קָם as perf. and part. of קוּם, see §72b and g; on יֵלֵד, &c., from ולד, see §69b.—On the weakening of ו and י to א, see §93x.
[25a] What vowels in Hebrew are unchangeable, i.e. are not liable to attenuation (to Šewâ), modification, lengthening, or shortening, can be known with certainty only from the nature of the grammatical forms, and in some cases by comparison with Arabic (cf. §1m). This hems good especially of the essentially long vowels, i.e. those long by nature or contraction, as distinguished from those which are only lengthened rhythmically, i.e. on account of the special laws which in Hebrew regulate the tone and the formation of syllables. The latter, when a change takes place in the position of the tone or in the division of syllables, readily become short again, or are reduced to a mere vocal Šewâ.
[25b] 1. The essentially long and consequently, as a rule (but cf. §26p, §27n, o), unchangeable vowels of the second and third class, î, ê, û, ô, can often be recognized by means of the vowel letters which accompany them (־ִי, ־ֵי, וּ, וֹ); e.g. יֵיטִיב he does well, חֵיכָל palace, גְּבוּל boundary, קוֹל voice. The defective writing (§8i) is indeed common enough, e.g. יֵיטִב and יֵטִיב for יֵיטִיב; גְּבֻל for נְבוּל; קֹל for קוֹל, but this is merely an orthographic licence and has no influence on the quantity of the vowel; the û in גְּבֻל is just as necessarily long, as in גְּבוּל.
As an exception, a merely tone-long vowel of both these classes is sometimes written fully, e.g. יִקְטוֹל for יִקְטֹל.
[25c] 2. The essentially or naturally long â (Qameṣ impure), unless it has become ô (cf. §9q), has as a rule in Hebrew no representative among the consonants, while in Arabic it is regularly indicated by א; on the few instances of this kind in Hebrew, cf. §9b, §23g. The naturally long â and the merely tone-long ā therefore can only be distinguished by an accurate knowledge of the forms.
- The Arabic, in such cases, often writes etymologically גַּלַי, but pronounces galā. So the LXX סִינַי Σινᾶ, Vulg. Sina; cf. Nestle, ZAW. 1905, p. 362 f. But even in Arabic שלא is written for שָׁלַו and pronounced salā.
- By vocales impurae the older grammarians meant vowels properly followed by a vowel letter. Thus כְּתָב kethâbh was regarded as merely by a licence for כְּתָאב, &c.