 Bolzano’s main work in theology is his four volume Textbook of the Science of Religion, which was published in 1834 by his pupils — without any mention of the author — from their very deficient lecture notes (much to Bolzano’s displeasure). What is meant by ‘science of religion’ (also ‘philosophy of religion’ or ‘philosophical doctrine of religion’), according to Bolzano, is the “science of the most perfect religion” (RW I, 3). Here Bolzano presupposes a concept of religion that is, to be sure, interesting, but not unproblematic from the Catholic standpoint. Bolzano starts with religion in the subjective sense, i.e., the religion of a person; this is, according to Bolzano, the set of religious opinions of this person. The content or “material” (Stoff) of a religion in the subjective sense is a religion in the objective sense. Thus, a religion in the objective sense is a set of propositions which can be grasped (in the sense of \(\mathbf{G}\) as explained in section 4.1) by a religion in the subjective sense. Bolzano’s concept of religion is consequently based on his definition of religious propositions or religious opinions: A proposition (and analogously also a subjective proposition or a judgment, an opinion etc.) is on Bolzano’s view religious iff it is both (generally) important and moral. A proposition is (generally) important iff it generally exerts influence on our virtue and happiness (RW I, 51 f.); and a proposition is moral iff “there is in the nature of man a reason for the temptation, without being justified in this, to acknowledge it either as true or as false” (RW I, 58). Thus, as a summary of Bolzano’s definition of the concept of religion in the subjective sense, the following may be stated: The religion of a person is “the collection of all those opinions of this person which manifest either an advantageous or a disadvantageous influence on his virtue or his happiness and are at the same time such that there was a special temptation, without any sufficient reason, to decide either in favor of or against them” (RW I, 60 f.).