The pa’al infinitive construct for most roots has the pattern sh’va-kholem: זְכֹר. When the final root letter is ה, that ה strengthens to a ת: בְּנוֹת. When the middle root letter is ו or י, that letter becomes a vowel: שׁוּב. For many roots that begin with י, as well as some that begin with ל or נ, the first root letter is lost and a ת is added to the end. The resulting form sounds like a segolate noun: שֶׁבֶת.