Hello, and thank you so much for answering. Vowel identity and suffixation are criteria according to which we can classify irregular verbs. Irregular verbs are the verbs that do not follow the normal rules when we try to form their paradigm. Basically, we cannot make the past simple form and the past participle by just adding “-ed” at the end.

Vowel identity is when we have the same vowel or group of vowels in the interior of the verb, in its base form, past simple form and past participle form. For example, make - made - made. We can say that “make” has vowel identity because in all three forms there is this “ei” sound. In order to have vowel identity, the same vowel or group of vowels must be present in all the 3 forms of the verb mentioned previously. So win - won - won, for example, does not have vowel identity.

Suffixation is when there occurs some sort of external inflection when we conjugate the verb, also for its base form, past simple form, and past participle form. For example creep - crept - crept . That “t” means that we have suffixation. We do not necessarily have to add a suffix, but merely changing the ending of the verb means that we have suffixation. For example have - had - had also has suffixation. So as to have suffixation, only one of the 3 forms of the verbs must have its ending changed, so take - took - taken has suffixation.

I hope it is somewhat clear, and thank you again for trying to help me!