Before an academical audience it behoved him to be circumspect; nor could he transgress the formal methods of scholastic argumentation.
Two principal subjects seem to have formed the groundwork of his teaching at this period.

The first was the doctrine of the Thirty Divine Attributes, based on S.Thomas of Aquino.

The second was Lully's Art of Memory and Classification of the Sciences.

This twofold material he worked up into a single treatise, called _De Umbris Idearum_, which he published in 1582 at Paris, and which contains the germ of all his leading speculations.

Bruno's metaphysics attracted less attention than his professed Art of Memory.