From the verb-stem (or theme) the present stem is formed in several ways. All verbs are arranged in the present system according to the method of forming the present stem from the verbstem. Verbs are named according to the last letter of the verb-stem ( cross376): 1. Vowel Verbs, 2. Liquid Verbs (including liquids and nasals), 3. Stop Verbs.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].