This articles attempts to confront “modernism” with Brentano’s rationalism, or rather his “rational theism”, especially as it is found in the work “On the origin of moral knowledge” in which ethical questions are closely linked to problems of religion. “Modernism” we characterise as basically an attempt to emancipate humanity by the power of a presuppositionless, critical Reason, which considers, in a new way, questions which were still “taboo” even during the enlightenment. In Brentano we start from the concepts of God and Love. In understanding them a whole raft of epistemological and methodological theses are involved, characteristic of Brentano practically from the time of his Psychologie… until his late work. One of our key conclusions is that Franz Brentano remained, with his rationalist belief in Providence, a critical follower of G. W. Leibniz and a “classic” modernist of the second half of the nineteenth century and the beginning of the twentieth.