The Opus Majus (Latin for "Greater Work") is the most important work of Roger Bacon. It was written in Medieval Latin, at the request of Pope Clement IV, to explain the work that Bacon had undertaken. The 878-page treatise ranges over all aspects of natural science, from grammar and logic to mathematics, physics, and philosophy. Bacon sent his work to the Pope in 1267. It was followed later the same year by a smaller second work, his Opus Minus, which was intended as an abstract or summary of the longer work, followed shortly by a third work, Opus Tertium, as a preliminary introduction to the other two.
Opus maius, 1750 edition
The Opus Majus is divided into seven parts:
Part one considers the obstacles to real wisdom and truth, classifying the causes of error (offendicula) into four categories: following a weak or unreliable authority, custom, the ignorance of others, and concealing one's own ignorance by pretended knowledge.
Part two considers the relationship between philosophy and theology, concluding that theology (and particularly Holy Scripture) is the foundation of all sciences.
Part three contains a study of Biblical languages: Latin, Greek, Hebrew, and Arabic, as a knowledge of language and grammar is necessary to understand revealed wisdom.
As a recent paper emphasizes, this major work cannot be usefully read exclusively in the context of the history of science and philosophy while forgetting to consider Bacon's religious commitment to the Franciscan Order. "His Opus maius was a plea for reform addressed to the supreme spiritual head of the Christian faith, written against a background of apocalyptic expectation and informed by the driving concerns of the friars. It was designed to improve training for missionaries and to provide new skills to be employed in the defence of the Christian world against the enmity of non-Christians and of the Antichrist".
^Opus Majus in year 1267 was accompanied by a letter of dedication to the Pope. The letter was found by F. A. Gasquet in the Vatican Library and published in 1897.
^Clulee, Nicholas H.; Vickers, Brian (1984). "At the crossroads of magic and science: John Dee's Archemastrie". In Vickers, Brian (ed.). Occult and scientific mentalities in the Renaissance. p. 59. doi:10.1017/CBO9780511572999.003. ISBN9780511572999.
^(p. 692) Power, Amanda. (2006). "A Mirror for Every Age: The Reputation of Roger Bacon". The English Historical Review. 121 (492): 657-692. doi:10.1093/ehr/cel102.