The missing letter rule assists the grammarian in finding the missing letter of the YQTL forms. Take note of the vowel under the prefix:
- If it is a sere, then the missing letter is from the beginning of the verb and is likely a yod (the verb הלך fits in this category as well).
- If it is a qamats, the missing letter will be from the middle of the root and will be a holem-vav, holem, or hiriq-yod (called hollow verbs).
- If a root appears to begin with the same two letters (via a dagesh-forte), then the missing letter is an initial nun. The nun assimilated into the following letter; and hence, the dagesh-forte.
- If the vowel is anything other than a sere or qamats, then the missing letter is from the end of the root and is a ה.
See KHW 3.1, 6.1a, 7.1a, and 12.1.