Gesenius' Hebrew Grammar/24. Changes of the Weak Letters ו and י
Philippi, Die Aussprache der semit. Konsonanten ו und י (mentioned above, §5b, note 1), a thorough investigation of their phonetic value as consonantal, i.e. non-syllabic, vowel-sounds, not palatal or labial fricatives; cf. also E. Sievers, Metrische Studien, i. 15.
24a ו and י are, as consonants, so weak, and approach so nearly to the corresponding vowels u and i, that under certain conditions they very readily merge into them. This fact is especially important in the formation of those weak stems, in which a ו or י occurs as one of the three radical consonants (§69 ff., § 85, § 93).
1. The cases in which ו and י lose their consonantal power, i.e. merge into a vowel, belong almost exclusively to the middle and end of words; at the beginning they remain as consonants.
The instances may be classified under two heads:
24b (a) When either ו or י with quiescent Šewâ stands at the end of a syllable immediately after a homogeneous vowel (u or i). It then merges in the homogeneous vowel, or more accurately it assumes its vowel-character (ו as u, י as i), and is then contracted with the preceding vowel into one vowel, necessarily long, but is mostly retained orthographically as a (quiescent) vowel letter. Thus הוּשַׁב for huwšab; יִיקַץ for yiyqaṣ; so also at the end of the word, e.g. עִבְרִי a Hebrew, properly ʿibrîy, fem. עִבְרִיָּה, pl. עִבְרִיִּים (and עִבְרִים); עָשׂוּ Jb 4125 for עָשׂוּו (cf. עֲשׂוּוֹת 1 S 2518 Kethîbh). On the other hand, if the preceding vowel he heterogeneous, ו and י are retained as full consonants (on the pronunciation see §8m), e.g. שָׁלֵו quiet, זִו the month of May, גּוֹי nation, גָּלוּי revealed. But with a preceding ǎ the ו and י are mostly contracted into ô and ê (see below, f), and at the end of a word they are sometimes rejected (see below, g).
Complete syncope of ו before î occurs in אִי island for אֱוִי; עִי ruins for עֲוִי; רִי watering Jb 3711 for רְוִי; [כּי burning Is 324 for כְּוִי, cf. §§84ac, e, 93 y]. 24c Thus an initial יְ after the prefixes בְּ, וְ, כְּ, לְ, which would then be pronounced with ĭ (see §28a), and also almost always after םִ (see §102b), coalesces with the ĭ to î, e.g. בִּֽיהוּרָה in Judah (for בִּיְ׳), וִֽיהוּדָה and Judah, כִּיאֹר as the Nile, לִֽיהוּדָה for Judah, מִידֵי from the hands of.
24d (b) When ו and י without a vowel would stand at the end of the word after quiescent Šewâ, they are either wholly rejected and only orthographically replaced by ה (e.g. בֶּ֫כֶה from bikhy, as well as the regularly formed בְּכִי weeping; cf. §93x) or become again vowel letters. In the latter case י becomes a homogeneous Ḥireq, and also attracts to itself the tone, whilst the preceding vowel becomes Šewâ (e.g. פְּרִ֫י from piry, properly pary); ו is changed sometimes into a toneless u (e.g. תֹּ֫הוּ from tuhw).
24e Rem. In Syriac, where the weak letters more readily become vowel sounds, a simple i may stand even at the beginning of words instead of יְ or יִ. The LXX also, in accordance with this, write Ἰουδά for יְהוּדָה, Ἰσαάκ for יִצְחָק. Hence may be explained the Syriac usage in Hebrew of drawing back the vowel i to the preceding consonant, which properly had a simple vocal Šewâ, e.g. (according to the reading of Ben-Naphtali) וִיֽלֲלַת Jer 2536 for וְיִֽלֲלַת (so Baer), כִּֽיתְרוֹן Ec 213 for כְּיִתְרוֹן, cf. also the examples in §20h, note 2; even וִיחֵ֫לּוּ Jb 2921 (in some editions) for וְיִ֫חֵלּוּ. According to Qimḥi (see §47b) יִקְטֹל was pronounced as iqṭōl, and therefore the 1st peps. was pointed אֶקְטֹל to avoid confusion. In fact the Babylonian punctuation always has ĭ for ä in the 1st pers.
24f 2. With regard to the choice of the long vowel, in which ו and י quiesce after such vocalization and contraction, the following rules may be laid down:
(a) With a short homogeneous vowel ו and י are contracted into the corresponding long vowel (û or î), see above, b.
24g Rem. The rejection of the half vowels ו and י (see above, b) occurs especially at the end of words after a heterogeneous vowel (ă), if according to the nature of the form the contraction appears impossible. So especially in 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.
- Or as consonantal vowels (see above), and are then transcribed by P. Haupt, Philippi, and others, as u̯, i̯, following the practice of Indogermanic philologists. וּ for וְ and, alone is a standing exception, see § 26. 1 and §104e. On י=i at the beginning of a word, cf. §47b, note. According to §19a, end, initial ו in Hebrew almost always becomes י; always in verbs originally פ״ו, §69a. Apart from a few proper names, initial ו occurs only in וָו hook, וָלָד child Gn 1130, 2 S 623 Kethîbh [elsewhere יֶ֫לֶד], and the doubtful וָזָד Pr 218.
- According to Abulwalid, Ben-Naphtali regarded the Yodh in all such cases as a vowel letter.
- Instances in which no contraction takes place after ă are, מַיְמִינִים 1 Ch 122; אַיְסִירֵם Ho 712 (but cf. §70b); הַיְשַׁר ψ 59 Qerê; the locatives בַּ֫יְתָה, מִצְרַ֫יְמָה, &c.—On the suffix ־ָ֫ יְכִי for ־ָ֫ יִךְ see §91l.—Sometimes both forms are found, as עַוְלָה and עוֹלָה; cf. חַי living, constr. state חֵי. Analogous is the contraction of מָ֫וֶת (ground-form mawt) death, constr. מוֹת; עַ֫יִן (ground-form ʿayn [ʿain]) eye, constr. עֵין.
- 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.