The Liber sex principiorum (or Liber de sex principiis) is an anonymous Latin work of philosophy from the late twelfth century. It aims to complement Aristotle's "Categories" by providing justifications for the six categories neglected by Aristotle in his scheme of ten categories. The "six principles" (categories) of the title are place, time, position, possession, action and passion (on top of substance, quality, quantity and relation). The "Liber" became one of the standard works of the "logica vetus" ('old logic') curriculum and by the mid-thirteenth century was erroneously ascribed to Gilbert de la Porrée. It was widely commented upon by medieval philosophers, including Robert Kilwardby, Nicholas of Paris, Martin of Dacia, Radulphus Brito, Peter of Auvergne and Thomas of Erfurt. Nevertheless, the complete text does not survive, only fragments.
There is a critical edition in .
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