What the Corpus Actually Contains, and Who Geber Was

The authorship problem does not diminish the work.

It sets out the sulphur-mercury theory of metallic composition, which structured alchemical thinking in Arabic and then in Latin for the better part of a millennium; a doctrine of mizan, the balance of the four qualities in a substance, worked out numerically; and a great deal of genuine laboratory procedure, distillation, crystallisation, sublimation, and the preparation of strong acids.

The Latin Geber is a further complication and a common source of error. The most influential Latin text under that name, the Summa perfectionis, is not a translation from the Arabic Jabir at all; it is a Latin composition of around 1300, which William Newman has argued in detail was written by Paul of Taranto. So the figure who stood for the whole art in medieval Europe, to the point that his Latinised name became a byword for obscure language, is at two removes from any historical person: a Latin author writing under an Arabic name that was itself the pen-name of a school.