Wilhelm Gesenius, Gesenius' Hebrew Grammar (1910)
“ It is there shown (1) that the sharpening of the 1st radical often serves to emphasize a particular meaning (cf. יִגָּר, but יְגֹרֵ֫הוּ, יָחֵל and יַחֵל, יִסֹּב and יָסֹב, יִשֹּׁם and תֵּשַׁם) , and elsewhere no doubt to dissimilate the vowels (as יִגָּר, יִדַּל, never יָגַר, יָדַל, &c.) : (2) that the sharpening of the 1st radical often appears to be occasioned by the nature of the first letter of the stem, especially when it is a sibilant. ”
