Guibert tied Easterners’ cleverness to their air and blamed intellectual agility for heresy.

Evidence

Apparently, these men, because of the purity of the air and sky in which they are born, as a result of which their bodies are lighter and their intellect consequently more agile, customarily abuse the brilliance of their intelligence with many useless commentaries. Refusing to submit to the authority of their elders or peers, “they searched out evil, and searching they succumbed” [Ps. 63:7]. Out of this came heresies and ominous kinds of different plagues. — John V. Tolan, Saracens, 785

Categorization

• QUESTION: Want to chase the classical/Arabic genealogy of this climactic-determinism — the idea that air and sky shape intellect is straight from ancient Greek environmental theory (Hippocrates’ Airs Waters Places). Did Guibert know that text directly or via some intermediary?
• XREF: Climatic determinism recurs across medieval geography — connects to later racial/geographic essentialism; also reverses the modern association where cleverness is praised, here it is the source of heresy.
• CANDY: Medieval author blames heresy on brainy people who live in clear air and read too many commentaries rather than submitting to their elders.