Gesenius' Hebrew Grammar/71. Verbs פ״י. Third Class, or Verbs with Yôdh assimilated
In some verbs פ״י, the Yôdh (or the original Wāw) does not quiesce in the preceding vowel, but is regarded as a full consonant, and, like Nûn,[1] is assimilated to the following consonant. These forms, therefore, belong properly to the class of strong verbs. Assimilation invariably takes place in יָצַע (prop. וצע) to spread under; Hiphʿîl הִצִּיעַ, Hophʿal הֻצַּע; יָצַת to burn, imperfect יִצַּת, Niphʿal נִצַּת, Hiphʿîl הִצִּית (in Is 274 also אַצִּיתֶ֫נָּה is to be read with König; in 2 S 1430 the Masora has rightly emended the Kethîbh והוציתיה, which could only be the 1st sing. perf. of a verb פ״ו, to the imperative וְהַצִּית֫וּהָ in agreement with the context and all the early versions); יָצַג, Hiphʿîl הִצִּיג to place, Hophʿal הֻצַּג; and probably also in the forms ordinarily derived from נָצַב, viz. נִצַּב (Niphʿal), הִצִּיב, יַצִּיב, הֻצַּב; at any rate a stem יָצַב is implied by the Hithpaʿēl הִתְיַצֵּב; instead of the anomalous וַתֵּֽתַצַּב Ex 24 read with the Samaritan ותתיצב, i.e. וַתִּתְיַצֵּב. Besides the common form we find once אֶצֹּק in Is 443 (from יָצַק to pour) with a transitive meaning, beside וַיֵּ֫צֶק intransitive, 1 K 2235. Elsewhere the imperfect consecutive has the form וַיִּצֹק Gn 2818, 3514, &c., cf. § 69 f, where also other forms of יָצַק are given; וַיִּ֫יצֶר and יִּצֹּר (Is 4412, 498, Jer 15 Qerê), from יָצַר to form, are, however, used in the same sense. Cf. also אֶסֳּרֵם Ho 1010; וַיִּשַּׁ֫רְנָה (for וַתִּ׳ according to § 47 k) 1 S 612; לִיסֹּד 2 Ch 317 (cf. § 69 n) and מוּסָּד Is 2816. This assimilation is found always with sibilants (most frequently with צ) except in the case of וַיִּקַּץ 1 K 315 (so ed. Mant., Ginsb., Kittel; but Jabl., Baer וַיִּקַץ) and in הֻ֫לֶּדֶת Gn 4020, Ez 165 (cf. הוּלֶּדֶת verse 4), infinitive Hophʿal of יָלַד (cf. נוּלְּדוּ § 69 t).