Form the perfect tense using the auxiliary verb 'haber' and a past participle. Irregular verbs in the perfect tense in Spanish The perfect tense is made of the verb 'haber' and a past participle.

Some past participles are irregular ... The first part of the perfect tense is the present tense of the verb haber, which is known as an auxiliary verb. An auxiliary verb, also called a helping ...

In your scientific paper, use verb tenses (past, present, and future ... such as an infinitive (to do) or a participle (doing), its subject is implied to be the subject of the clause, or sometimes ...