Galen's intellectual autobiography, On my own opinions, has challenged, and frustrated, potential editors for over a century. It is preserved in Greek excerpts, in a Latin translation made from the Arabic and with a spurious conclusion, and, for its last three chapters, in a passage of continuous Greek that circulated under the misleading title of On the substance of the natural faculties. Around 1340, the Italian translator Niccolo da Reggio made an extremely faithful Latin version from a Greek manuscript of (...) the last two chapters. Although by itself no one source offers a complete text of the treatise, together they apparently cover it in its entirety. The Latino-arabic version, called variously De sententiis, De sententiis medicorum, and De credulitate Galeni, is the most extensive, but, as a comparison with the surviving Greek shows, it frequently departs considerably from the wording, and even general meaning, of the Greek. Indeed, without the availability of many parallel passages elsewhere in the Galenic corpus, much of this Latin translation would remain unintelligible. (shrink)