 Early lists of works, such as the Stams Catalogue, attribute to Kilwardby the De unitate formarum, De physica, and De metaphysica, whereas Nicholas Trivet mentions the treatise De universali. This latter work is possibly a reference to a passage in Kilwardby’s Notule Libri Posteriorum—“Hec est pars in qua Aristotiles determinat de uniuersali” (Cannone 2002, 132)—which might have circulated isolated from the rest of the work. In the same way, the work De unitate formarum clearly is the last (7th) article of Kilwardby’s answer to a letter sent to him by Peter of Conflans, and it is found alone in some manuscripts.