I have been studing German irregular verbs in the present tense, specially those that change the stem vowel when conjugaten into second and third person singular, such as a>ä , e>i , e>ie , au>äu , o>ö , ä>ie .
The book I am using to study has a really brief explanation about the subject.
So, here is one thing I realized and I am trying to make sure I got right, as I am a beginner and I am not so familiar with German words pronounciation:
01. Irregular verbs with stem vowel e that turn into ie have always a long stem vowel in the infinitive form (e.g. lesen, befehlen, empfehlen, geschehen, sehen, stehlen);
02. Irregular verbs with stem vowel e that turn into i have a short stem vowel in the infinitive form (e.g. essen, fressen, messen, schmelzen, vergessen, berste, fechten, flechten, schelten, bergen, brechen, dreschen, helfen, melken, quellen, schrecken, schwellen, sprechen, stechen, sterben, treffen, verderben, werben, werfen) except for the verbs gelten, nehmen, treten, werden, geben.
Is it right? Identifying these little patterns really help me to memorize these verbs, so if anyone want to share another point about this subject, I would appreciate it.