In 1597 Francisco Suárez published a comprehensive treatise on beings of reason (entia rationis) as part of his Disputationes metaphysicae. Subsequent scholastic philosophers vigorously debated various aspects of Suárez’s theory. The aim of this paper is to identify some of the most controversial points of these debates, as they developed in the first half of the seventeenth century. In particular, I focus on the intension and the extension of ‘ens rationis’, its division (into negations, privations and relations of reason) and its causes. Additionally, I will discuss how Suárez’s views sparked a number of debates within the classical view, debates which ultimately led to the emergence of various alternative theories, especially among the Jesuits. These non-classical views radically revise the previous classical conception of beings of reason.