The accusative and infinitive is the usual grammatical construction by means of which Classical Latin expressed indirect statements, that is, statements which report what someone has said, thought, felt, etc. Whereas a direct statement would say the indirect statement might say Classical Latin tends not to use a conjunction equivalent to the English "that" to introduce indirect statements. Rather, an accusative subject is used with an infinitive to develop the appropriate meaning. For example, translating the aforementioned example into Latin: Sē here is an accusative reflexive pronoun referring back to the subject of the main verb i.e. Iūlia ; esse is the infinitive "to be." Note that the tense of the infinitive, translated into English, is relative to the tense of the main verb. Present infinitives, also called contemporaneous infinitives, occur at the time of the main verb. Perfect infinitives occur at a time before the main verb. Future infinitives occur at a time after the main verb. For example, the contemporaneous infinitive in this sentence, would still be translated "They said he was helping her," even though iuvāre is a present infinitive. Passive periphrastic infinitives, i.e. the gerundive + esse, indicate obligatory action in indirect statements, e.g. Gāius dīcit litterās tibi scrībendās esse, "Gaius says that the letters ought to be written by you." In late classical and Medieval Latin, the ACI gradually gave way to a construction with quod with the subjunctive. This was probably the more common usage in spoken Latin and is the form used consistently in Jerome's Vulgate, which reflects a colloquial style. It is also the equivalent of the Greek indirect statement introduced by ὅτι. This is the origin of the construction in the modern Romance languages such as French:
In English and Spanish
In English, the ACI construction occurs with verbs of wishing, saying and perceiving as well as in causative clauses. Depending on the valency of the main verb in the sentence, English may use a full infinitive or a bare infinitive. The verbs make, see and hear have the interesting characteristic of using a bare infinitive in the active voice and a full infinitive in the passive: In Spanish, the ACI is used in causatives as well and in perception verbs, but it is not permitted in other cases. For example, in English one may say I told him to do it, but in Spanish one must say Le dije que lo hiciera "I said to him that he do it", not *Le dije hacerlo or any other construction with the infinitive. In the framework of transformational grammar, this construction is known as exceptional case-marking.
