A good article on Modernism can be found here. Here is a 'taster'...
IS MODERNISM STILL ACTIVE IN THE CATHOLIC CHURCH? (PART 1)
[The following quotations from the Encyclical Letter Pascendi Dominici gregis of Pope Pius X are taken mainly from the translation that appeared originally in the London Tablet and is reproduced in Claudia Carlen, ed., The Papal Encyclicals, vol. 3. pp. 71-98.]
1. Introduction. On September 8, 1907, Pope Saint Pius X published the encyclical letter Pascendi Dominici gregis, in which he condemned the heresy of Modernism, a heresy which he defined as "the synthesis of all heresies" (Pascendi, no. 39). From then until the Second Vatican Council there was great effort on the part of the Hierarchy to oppose and wipe out this heresy. Among other things the Oath against Modernism of September 1, 1910, was required each time that a member of the Church received a sacred order or a pastoral ministry such as bishop of a diocese, pastor of a parish, seminary professor, preacher, religious superior, official of a diocese or of the Holy See, or to receive an ecclesiastical degree. But around the time of the Second Vatican Council, the requirement to take this oath was suppressed by the Holy See, and it has never been seen again. To the best of my knowledge, no published reason or rationale for the removal of this requirement was given, but the assumption is that there was no longer a sufficient reason to keep it in use. Yet, many of the same manifestations within and without the Catholic Church that motivated Pope Pius X to write the Encyclical seem to be in some ways still present today and in many ways even more present today than they were in the early twentieth century. Was the "Modernism" observed by Pius X in 1907 just an illusion? Did it address a situation that was not really existing? Or was there a real movement that ceased afterwards to have the same relevance that it had had before? These are questions that it might behoove us to consider. We could begin by taking some of the general characteristics and specific instances of Modernism described in the Encyclical and compare them with apparently similar instances that seem to have continued to exist in the Church up to the present day, in order that we might see if there is a real difference between them and in what this difference might consist.2. Reformers of the Church. In opening the description of Modernism and Modernists in his encyclical Pascendi, Pope Pius X remarks that there are in the Church many lay persons and priests "who, feigning a love for the Church, lacking the firm protection of philosophy and theology, nay more, thoroughly imbued with the poisonous doctrines taught by the enemies of the Church, and lost to all sense of modesty, vaunt themselves as reformers of the Church" (Pascendi no. 2). The Pope remarks that these Modernists "lay the axe, not to the branches and shoots, but to the very root, that is, to the faith and its deepest fibres," and that "there is no part of Catholic truth from which they hold their hand, none that they do not strive to corrupt." He goes on to say that the Modernists "double the parts of rationalist and Catholic, and this so craftily that they easily lead the unwary into error." They "possess, as a rule, a reputation for the strictest morality" and "relying upon a false conscience, they attempt to ascribe to a love of truth that which is in reality the result of pride and obstinacy" (Pascendi no. 3).3. Faith Is a Feeling. As philosophers, Modernists are agnostics inasmuch as they hold that to know the existence of God is not within the capability of human reason or "the direct object of science," and that God is not to be considered a subject of history (Pascendi no. 6). Hence, they say, faith is a feeling (sensus) that arises from a felt need of the divine whose roots lie hidden in the subconscious, where also the roots of divine revelation lie (Pascendi no. 7). They make religious consciousness the law to which all must submit, even the supreme authority of the Church (Pascendi no. 8). The religious unknowable presents itself in the form of some mysterious phenomenon or some man whose character, actions, and words cannot, apparently, be reconciled with the ordinary laws of history" (Pascendi no. 9).4. The Evolution of Dogma. From this philosophy the Modernists derive three principles which "constitute the foundation of historical criticism." For example, in the case of the Person of Jesus: a) whatever in his history is suggestive of the divine must be rejected; b) every element that raises Him above historical conditions must be removed; c) every element is also to be removed that is not in keeping with the character, circumstances, and education of Jesus, and with the place and time in which He lived (Pascendi no. 9). Modernists say that "what we call dogmas are liable to change," since religious formulas "have no other purpose than to furnish the believer with a means of giving an account of his faith to himself" (Pascendi no. 12). And thus "the way is open to the intrinsic evolution of dogma," since these formulas, "should be living, and should live the very life of the religious sense" (Pascendi no. 13).
Click here for more. It is important to know what 'modern' Catholics are up against. Modernists live in the 'real world' but do not give assent to the truths of Divine Revelation, preferring a mere human philosophy that is fundamentally disassociated from the fullness of the 'real' Faith as possessed by the Catholic Church, to which we, as members of the faithful are called to give assent for our Salvation.