Indirect speech (ōrātiō oblīqua) is the way in which speech is reported without being directly quoted. For example, contrast "She said 'I saw him the other day'" with "She said that she had seen him the other day." In Latin, the same grammatical structure is used for complentizer clauses as well, such as "I know he wasn't there."
There are two different structures that can form an indirect speech clause in Latin: the accusative + infinitive construction, and the use of a subordinating conjunction.
This is the original type and the most common. It is comparable to English sentences like "I know him to be a good man", but whereas in English this construction is limited in use, in Latin it was the usual way to form such a sentence.
For the purposes of this example, we'll start with an independent clause, and then transform it into indirect speech. Take the sentence Trāns flūmen sunt lupī, meaning "There are wolves across the river." In this sentence, the word lupī, "wolves", appears in the nominative case. This is the case used for subjects. The verb, sunt, is conjugated for the third person present indicative.
To make this into indirect speech, the subject is put into the accusative case, and the verb into the infinitive (thus the name "accusative + infinitive"). Additionally, a verb is needed to introduce the clause, usually one of speech or perception. For this example, we'll use the verb videō, "I see". Our sentence becomes Videō trāns flūmen esse lupōs, "I see there are wolves across the river." The verb sunt is now the present active infinitive esse, and lupī is now the plural accusative lupōs.
This construction is less common. It uses one of the following conjunctions:
- quod - because
- quia - because
- quoniam - since
- quīn - that (complementizer; in negated sentences of doubt, knowledge, etc.)
followed by a subjunctive phrase. As can be seen from the definitions above, these conjunctions (except quīn) were not originally complementizers. As Latin evolved, their meaning weakened in certain constructions, leading to their use for indirect speech.
We could rewrite our accusative + infinitive sentence above as Videō quia trāns flūmen sint lupī. Notice that the only change from the independent form is that the verb is now in its subjunctive form.
This construction is the one that survives in modern Romance languages (although most use the indicative, not the subjunctive).