A verb expresses an action or state of being and is generally shown in its infinitive, which is the basic “to” form, as in to “to be.” An infinitive is the form of the verb before it has been conjugated.
Table 1 shows an example of the irregular verb “to be” conjugated in English.
Even in English, each subject has its own matching verb form that never changes and can't be mixed and matched with other verb forms.