In what matters may faith and the Church be a guide to research in this negative sense? In all fields, or only some? Evidently only in their own sphere. But to the sphere of faith belongs only what is contained in divine revelation, viz., the truths of _religion and morality_, as laid down in Scripture and tradition, the truths of God and His work of salvation, of man and his way to his eternal destiny, of the means of grace, and of the Church. Whatever lies outside of that sphere does not belong to the province of faith. This is true also of the teaching authority of the Church. The purpose of the Church is to guard faithfully the treasure of divine revelation and to transmit it in an authoritative manner to mankind: hence her authority in teaching is confined to what is contained in revelation, and what is necessary for an efficient custody and transmission of it to mankind. Hence she may declare certain truths as revealed, she may reject opposing errors, she may condemn books offensive to faith, she may approve or reject systems of ethics. But she cannot set up wholly new religious truths or revelations. _Depositum custodi_—this is the purpose of the Church. Still less are matters of an entirely profane nature subject to the teaching authority of the Church. Profane sciences can therefore receive direction from faith only in those matters which at the same time belong to the province of faith. What follows from this? It follows that _almost all the profane sciences are incapable of being instructed or restricted by faith_, because their province lies outside that of faith, and does not come in touch with it: they are left to themselves to correct their errors. When the astronomer in his observatory watches the movements of the planets, and bases thereon his mathematical calculations, when the physicist or chemist in his laboratory observes the laws of nature or makes new discoveries, when the pathologist studies the symptoms of diseases in organisms, no warning voice interrupts their work of study. Of course when they deny the creation, the possibility of miracles, then they conflict with faith; but then they have ceased to be naturalists, they have become philosophers. When the botanist or zoölogist in his laboratory is studying plants and animals and collecting his specimens, when the palæontologist is excavating and examining his fossils, they enjoy perfect freedom: all this has nothing directly to do with faith. And there is no warning sign set up for the geographer or geologist when settling the orographical or hydrographical conditions of countries or measuring geological strata; no danger signal disturbs the linguist in establishing the grammar of unknown languages, nor the archæologist or the historian, when they discover new documents or decipher inscriptions. Nor does anybody interrupt the mathematician in his calculations.