 It was a matter of dispute how first and second intentions differ, what they refer to and what their ontological status is, a dispute bordering on epistemology and the philosophy of mind. Important participants in this discussion are Roger Bacon, who defines intentions as intelligible species, that is, mental likenesses of things, and Hervaeus Natalis and Peter Aureoli, who (apart from disagreeing on many issues) both hold that intentions are neither identical with extramental things nor with qualities of the intellect; they have their own “intentional being” (esse intentionale), which is the result of a cognitive act (Perler 1994). This position was criticized both by nominalists and realists: the nominalist William of Ockham objected against the reification of intentions and held that intentions are always natural signs in the mind; second intentions are natural signs which signify other natural signs (Summa logicae I.12); the realist author Walter Burley rejects the idea of a special being of intentions and argues that second intentions are part of extramental reality (Knudsen 1982). Logic as the science of second intentions continued to be a philosophical topic well into the sixteenth century, especially among Thomists and Scotist authors.