Some simple rules to follow that help:
- No Hebrew verbs begin with two of the same letter. For example, תתן doesn’t exist, so any verb that has a dagesh in the middle radical is most probably a I-Nun.
- Missing root letter + vowel under preformative (not tsere or qamets) = III-He verb.
- Missing root letter + tsere under preformative + missing letter = 1st root letter is missing; it’s probably a yod (I-yod).
- Missing root letter + qamets under preformative = 2nd letter missing, hollow verb
- If there is only one root letter showing = prob I-Nun and III-He.
- Most III-He verbs were originally III-Yod verbs – so in many III-He forms the He drops out and the original yod returns.
- a taw at the end of a verb = infinitive of a I-yod, I-waw or I-nun.