Transitivity shows how the verb organizes the sentence's complements and, therefore, helps identify whether there is a direct object, indirect object, or no object. Some verbs require a complement to complete the sense, others appear on their own, and some may alternate between these uses depending on the construction. The classification also intersects with the conjugation in -ar, -er, and -ir, but the ending does not determine transitivity. The form of the verb and the presence of a preposition must be observed together to recognize the syntactic function.

Direct-transitive verbs require a direct object, i.e., an object without a preposition required by the verb. This object receives the verbal action directly and answers, often, the questions what or whom. Verbs such as read, buy and visit usually fall into this group, though real usage may vary depending on context and register.

The indirect-transitive verb requires an indirect object introduced by a preposition. In this case, the preposition is part of the verb's regency and cannot be removed without changing the structure. Verbs such as gostar de, precisar de, and obedecer a show this pattern, which is central to the syntactic analysis of Regular Verbs and Irregular Verbs.

Bitransitive verb has two complements: a direct object and an indirect object. This construction is common in verbs such as give, offer, and send, which transfer something to someone. The relationship between the two objects is usually clear, because one receives the thing and the other receives the recipient.

The intransitive verb does not require an object to complete the meaning. It can appear with time, place, or manner adjuncts, but these elements are not objects required by the verb. Verbs such as arrive, sleep, and run are often intransitive, though some verbs change behavior depending on usage.

The ambitransitive verb can function as transitive or intransitive depending on the construction. In these cases, the presence or absence of an object alters the sentence's organization, but not necessarily the core meaning. Verbs such as open, close, and increase show this alternation in frequent uses.

The pronominal verb occurs with an unstressed pronoun attached to the verb, and this pronoun is part of the verbal construction. In many cases, the verb does not maintain the same behavior without the pronoun, as in lembrar-se and queixar-se. This group closely relates to Reflexive Verbs, although not every pronominal verb has strictly reflexive value.

The endings in -ar, -er, and -ir organize the conjugation paradigms, but they do not determine whether a verb is transitive, intransitive, or pronominal. Therefore, verbs with the same ending can have different syntactic behaviors. The correct analysis depends on regency (valency), the complement, and the context.

Ser is a fundamental and very frequent irregular verb in Portuguese. It appears in constructions of identity, classification, and time, and for this reason its use should be recognized early. Its inflection presents irregular forms, which makes it resemble other basic verbs such as Irregular Verbs.

Estar is another central irregular verb, widely used for states, locations, and progressive constructions. In Portugal, the structure estar a + infinitive is particularly frequent, while in Brazil the gerund is more productively used. This difference also appears in Verbal Periphrases and in Verbal Gerund.

Ter is an irregular verb of high frequency and functions both as a full possessive verb and as an auxiliary in compound tenses. Its presence is decisive for structures that depend on participles and periphrases, such as in Compound Tenses. It also appears in modal constructions expressing obligation or necessity.

Ir is a very frequent irregular verb and is essential in meanings of movement and near future. In the construction ir + infinitive, it forms a verbal periphrase that marks intention or posteriority. This combination is central to Verbal Periphrases.

Dar is an irregular verb of very high frequency and appears in transitive, ditransitive, and idiomatic constructions. Its own inflection deserves attention because the verbal form repeats itself in very different uses. In sentences with direct and indirect objects, it is one of the most useful models for recognizing Causative Verbs.

Dizer is a representative irregular verb, very frequent in speech and writing. It can introduce reported speech, direct object, and structures with indirect object depending on regency. Its form also helps to recognize the behavior of the most productive irregular verbs in Portuguese.

Non-finite forms include the infinitive, gerund, and participle, and are essential in Verbal Participles, Verbal Gerund, and Compound Tenses. The infinitive ends in -ar, -er, or -ir; the gerund ends in -ando, -endo, or -indo; and the participle can be regular in -ado or -ido, or irregular in forms such as feito and escrito. These forms do not mark person directly and serve as the basis for locutions and complex constructions.

Verbal periphrases combine an auxiliary verb with a non-finite form to create a single verbal value. Among the most frequent structures are ir + infinitive, estar + gerund, ter de + infinitive and continuar a + infinitive. In Portugal, estar a + infinitivo is very common, while in Brazil the gerund appears more frequently in equivalent uses.

Transitivity allows distinguishing verbs that require a direct object, an indirect object, both, or no complement. It is also necessary to recognize ambitransitive, pronominal, and irregular verbs, in addition to non-finite forms and the locutions that broaden verbal behavior. With this reading, it becomes possible to identify the function of each verb in the sentence and to predict the most likely valency (subcategorization frame) in common use.