The paper deals with the development in the usage of verbal moods following verba opinandi in preclassical and classical French. An evident change in mood usage following these verbs had taken place in the 17th century, namely a decline of the subjunctive in favour of the indicative, which became the norm in affirmative sentences by the end of the century. The aim was to verify theoretical information from old and historical grammars on the evidence of authentic texts in FRANTEXT, a set of French diachronic corpora. This research enabled the derivation of statistics to identify a turning point in the development, which appears to be around the year 1640. It also revealed distinctions between different sentence types in respect of the indicative/subjunctive ratio. Whereas affirmative sentences tend towards the indicative as the only possible mode, the subjunctive is retained in negations, questions and conditionals, since these sentence types exhibit a more negative epistemic modality, typically expressed with the subjunctive.