...the paradox of this Encyclical, and indeed of the modernism conflict in general, is that whilst a variety of thinkers clearly shared some of the ideas condemned, it was really only through this Encyclical that ‘modernism’ as a coherent and unified body of thought can be said to have existed.
Pascendi in many ways constructs modernism as a straw man in order to defend a certain style of philosophy and theology that had been designated as official for the Catholic Church by Pope Leo XIII in his 1879 Encyclical Aeterni Patris: that of Saint Thomas Aquinas. The dominance of this style had been reinforced by a resurgence of interest in Aquinas in the nineteenth century from the movement that became known as Neo-Thomism. Important centres for the propagation of Thomistic ideas developed in Europe and their influence was felt on the various letters and decrees issued by the Church against modernist trends in philosophy and theology at the end of the nineteenth and beginning of the twentieth century.
However, the roots of what is termed ‘philosophical modernism’ lie well before the modernist crisis of the twentieth century. In fact, one has to trace them back to the break-up of the medieval synthesis in theology and philosophy that was ushered in by Nominalism in the eleventh century. Nominalism was a philosophical movement that held that it was not possible to know universals or general realities, but that all one could safely come to know and to talk sensibly about were particulars. The tendency towards this thought led to a disbelief in a realist approach to the world and so too the view that one could come to know God in and through sensible reality. This breakdown of the medieval synthesis of thought was further intensified by scientific advances which gradually discredited the Aristotelian conception of the universe.
Re the modern idea that one can come to know God in and through sensible reality, cf. Prof. Harrison's discussion of scientia/science. It's difficult for us, from our 21st Century perspective, to remember that the original modernists saw themselves as religious reformers, and not as opponents of the Faith.