 Class IV verbs end in "-ia" or "-ua" in the present, but lose their final "a" in all the other tenses (including the subjunctive), and add a "j" in the past and perfect.Class I includes a sub-class of mutating stems that end in the present and subjunctive in "-wa", "-ua", "-ya" or "-ia".These change to "-j-", "-uj-", "-sh-" and "-ish-", respectively, in the past and perfect.