Check in your grammar books or dictionaries ... As you can see from the beginning of this alphabetical list, many common verbs in English are irregular and I am afraid it is a matter of learning ...

Irregular verbs don’t follow the usual pattern in the preterite tense. Some verbs in the preterite tense have irregular spellings when using the third person singular or plural forms.

In this sentence, the subject is Matt and Nate, which is plural; thus, we have to change our verb to eat. A regular verb is one that conforms to the rules of grammar, whereas an irregular verb ...