In Present tenses^x, Pronouns^x, Auxiliaries^x

 I think it's a big mistake because the verb after the auxiliary is in the past participle, it means that the auxiliary should be 'has'  (the verb 'to have' in the present) instead of 'is' (the verb 'to be'  in the present. its a common mistake and it's a...

Just change it into "I must go" - then it's easier to analyze: "go" here is the full verb that is in its infinitive and follows the modal auxiliary must - without to! I have to go: "have to" is the substitute form for "must", "go" again is the full verb in its infinitive. "Have to" here is a...