Ailly, Pierre D' (1350–1421)

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Pierre d'Ailly, the Ockhamist philosopher, was born at Compiègne in France. He studied at the Navarre College in Paris in 1372, receiving his doctoral degree in 1380 and becoming chancellor of the university in 1389. He was made bishop of Puy in 1395 and bishop of Cambrai in 1396 and cardinal in 1411. He took a leading part in the Council of Constance (14141418), where he asserted the superiority of a general council of the church over the pope. He died as papal legate at Avignon.

D'Ailly's literary output was vast and wide-ranging. It comprehended philosophy, theology, scientific theory, political theory, canon law, and ecclesiastical politics and touched on mysticism. Among his more important writings were the treatise De Anima, commentaries on Boethius's Consolation of Philosophy and the four books of the Sentences, two studies of mysticism and asceticism, three works on different aspects of church government, and a series of works on logic, astronomy, and geography.

In his philosophical outlook d'Ailly seems to have been sympathetic to Ockhamism. Like so many fourteenth-century thinkers he postulated different degrees of certainty. The main distinction d'Ailly made was between what he called "natural light" and reason. Natural light corresponded to knowledge that was indubitablenamely, that which could be reduced to the principle of contradiction or immediate intuition of the existence of the self, in the manner of John of Mirecourt. Reason, on the other hand, was only relative in its certainty and was confined to the natural order. Included within it were the traditional arguments for God's existence, which d'Ailly treated as merely probable. The influence of William of Ockham is also apparent in d'Ailly's treatment of God's omnipotence; since it was independent of the natural order, God was in no way bound to follow nature's laws. Accordingly, God could create the illusion that something existed when in fact it did not; this was one of the most insistent Ockhamist arguments against the infallibility of experiential knowledge. At the same time d'Ailly was careful to distinguish the realm of God's absolute power (potentia absoluta ) from the realm subject to his ordained power (potentia ordinata ). Whereas the first realm referred to God's omnipotence as such, the latter constituted the specific application of his omnipotence to this world; it provided the laws by which creation was regulated, and among them d'Ailly included the laws of physics. They therefore operated constantly and with certainty.

D'Ailly's debt to Ockham and John of Mirecourt is also to be seen in his views on essences. There was no inherent reason why hot was hot or cold cold other than God's willing it. The same applied to the moral order, where good and bad were such because of God's voluntary decree: "Nothing is good or bad of itself such that God must love or hate it." Similarly, a man was just not from possessing the intrinsic property of justice but because God accepted him as just. Here was the same absence of a constant scale of values that had proved so destructive of the traditional teachings in the time of Ockham and the first generation of his followers, who included Robert Holkot, Adam of Woodham, and John of Mirecourt. D'Ailly further emphasized the uncertain nature of natural experience by his acceptance of the so-called complexe significabile, by which an expression such as "sin" did not denote a specific object but was a description or statement that referred to an action. As employed by Nicolas of Autrecourt, it had denied the reality of a wide range of expressions. Thus the word God stood not for a specific being but for a verbal expression: supreme or highest being. As such it lacked correspondence to anything but a grouping of words. At the same time, in keeping at the natural level, d'Ailly granted a correspondingly wider area of jurisdiction to faith. Thus evidence for God's existence could be held only as a matter of belief.

See also Holkot, Robert; John of Mirecourt; Nicolas of Autrecourt; Ockhamism; William of Ockham; Wodeham, Adam.


works by d'ailly

Tractatus Exponibilium Magistri Petri de Allyaco. Paris, 1494.

Quaestiones Super Primum, Tertium et Quartum Sententiarum. Venice, 1500.

De Anima. Paris, 1501.

Tractatus et Sermones. Douai, France, 1639. Includes De Anima.

Destructiones Modorum Significandi. Conceptus et Insolubilia Secondum Viam Nominalium Magistri Petri de Allyaco. (No date.)

works on d'ailly

Dictionnaire de théologie catholique. Vol. I, 642654. Paris, 19031951.

Gandillac, M. P. de. "Usage et valeur des arguments probables chez Pierre d'Ailly." Archives d'histoire doctrinale et littéraire 8 (1933): 4391.

Gordon Leff (1967)