24 Therefore, venerable brethren, as often as We contemplate the good, the force, and the singular advantages to be derived from his philosophic discipline which Our Fathers so dearly loved. We think it hazardous that its special honor should not always and everywhere remain, especially when it is established that daily experience, and the judgment of the greatest men, and, to crown all, the voice of the Church, have favored the Scholastic philosophy. Moreover, to the old teaching a novel system of philosophy has succeeded here and there, in which We fail to perceive those desirable and wholesome fruits which the Church and civil society itself would prefer. For it pleased the struggling innovators of the sixteenth century to philosophize without any respect for faith, the power of inventing in accordance with his own pleasure and bent being asked and given in turn by each one. Hence, it was natural that systems of philosophy multiplied beyond measure, and conclusions differing and clashing one with another arose about those matters even which are the most important in human knowledge. From a mass of conclusions men often come to wavering and doubt; and who knows not how easily the mind slips from doubt to error? But, as men are apt to follow the lead given them, this new pursuit seems to have caught the souls of certain Catholic philosophers, who, throwing aside the patrimony of ancient wisdom, chose rather to build up a new edifice than to strengthen and complete the old by aid of the new-ill-advisedly, in sooth, and not without detriment to the sciences. For, a multiform system of this kind, which depends on the authority and choice of any professor, has a foundation open to change, and consequently gives us a philosophy not firm, and stable, and robust like that of old, but tottering and feeble. And if, perchance, it sometimes finds itself scarcely equal to sustain the shock of its foes, it should recognize that the cause and the blame lie in itself. In saying this We have no intention of discountenancing the learned and able men who bring their industry and erudition, and, what is more, the wealth of new discoveries, to the service of philosophy; for, of course, We understand that this tends to the development of learning. But one should be very careful lest all or his chief labor be exhausted in these pursuits and in mere erudition. And the same thing is true of sacred theology, which, indeed, may be assisted and illustrated by all kinds of erudition, though it is absolutely necessary to approach it in the grave manner of the Scholastics, in order that, the forces of revelation and reason being united in it, it may continue to be "the invincible bulwark of the faith."(38)
Source: Aeterni Patris (Vatican.va)