 There are two different sources for axiomatic works in the Middle Ages: Euclid and Proclus. For Proclus the axiomatic form mirrors the metaphysical structure of emanation. As all being emanates from the One, all propositions are derived from axioms. In his commentary on Euclid, Proclus contends that the scientific structure in which all propositions are proved from first principles is peculiar to the mathematical sciences, as befitting the middle status of mathematics between metaphysics and physics. Two important axiomatic works, Boethius’ De Hebdomadibus and Alan of Lille’s Regulae Caelestis Iuris, seem to follow both Proclus’s Elements of Theology, taking Neoplatonic metaphysical principles as their axioms, and the model of deriving conclusions from those principles, the method Proclus attributes to Euclid and to mathematics alone. The axiomatic form in Euclid is more complex, relying not just on first principles (communis animi conceptio), the only type of principle used by Boethius and Alan, but also on definitions, petitiones, theorems, etc. Euclid is the model for Nicholas of Amiens’s Ars Catholicae Fidei. However, even when thinkers like Nicholas of Amiens use the Euclidean axiomatic model, they are still relying on the justification and principles of Neoplatonic metaphysics, grounding the form in the metaphysics of emanation.