This is a passage taken from Pope Pius X's encyclical Pascendi. In this passage, he describes the philosophical foundations of the heresy of Modernism, namely "agnosticism" and "vital immanence."
Modernists place the foundation of religious philosophy in that doctrine which is usually called Agnosticism. According to this teaching human reason is confined entirely within the field of phenomena, that is to say, to things that are perceptible to the senses, and in the manner in which they are perceptible; it has no right and no power to transgress these limits. Hence it is incapable of lifting itself up to God, and of recognising His existence, even by means of visible things. From this it is inferred that God can never be the direct object of science, and that, as regards history, He must not be considered as an historical subject. Given these premises, all will readily perceive what becomes of Natural Theology, of the motives of credibility, of external revelation. The Modernists simply make away with them altogether; they include them in Intellectualism, which they call a ridiculous and long ago defunct system. Nor does the fact that the Church has formally condemned these portentous errors exercise the slightest restraint upon them. Yet the Vatican Council has defined, "If anyone says that the one true God, our Creator and Lord, cannot be known with certainty by the natural light of human reason by means of the things that are made, let him be anathema" (De Revel., can. I); and also: "If anyone says that it is not possible or not expedient that man be taught, through the medium of divine revelation, about God and the worship to be paid Him, let him be anathema" (Ibid., can. 2); and finally, "If anyone says that divine revelation cannot be made credible by external signs, and that therefore men should be drawn to the faith only by their personal internal experience or by private inspiration, let him be anathema" (De Fide, can. 3). But how the Modernists make the transition from Agnosticism, which is a state of pure nescience, to scientific and historic Atheism, which is a doctrine of positive denial; and consequently, by what legitimate process of reasoning, starting from ignorance as to whether God has in fact intervened in the history of the human race or not, they proceed, in their explanation of this history, to ignore God altogether, as if He really had not intervened, let him answer who can. Yet it is a fixed and established principle among them that both science and history must be atheistic: and within their boundaries there is room for nothing but phenomena; God and all that is divine are utterly excluded. We shall soon see clearly what, according to this most absurd teaching, must be held touching the most sacred Person of Christ, what concerning the mysteries of His life and death, and of His Resurrection and Ascension into heaven.
7. However, this Agnosticism is only the negative part of the system of the Modernist: the positive side of it consists in what they call vital immanence. This is how they advance from one to the other. Religion, whether natural or supernatural, must, like every other fact, admit of some explanation. But when Natural theology has been destroyed, the road to revelation closed through the rejection of the arguments of credibility, and all external revelation absolutely denied, it is clear that this explanation will be sought in vain outside man himself. It must, therefore, be looked for in man; and since religion is a form of life, the explanation must certainly be found in the life of man. Hence the principle ofreligious immanence is formulated. Moreover, the first actuation, so to say, of every vital phenomenon, and religion, as has been said, belongs to this category, is due to a certain necessity or impulsion; but it has its origin, speaking more particularly of life, in a movement of the heart, which movement is called a sentiment. Therefore, since God is the object of religion, we must conclude that faith, which is the basis and the foundation of all religion, consists in a sentiment which originates from a need of the divine. This need of the divine, which is experienced only in special and favourable circumstances, cannot, of itself, appertain to the domain of consciousness; it is at first latent within the consciousness, or, to borrow a term from modern philosophy, in the subconsciousness, where also its roots lies hidden and undetected.
Should anyone ask how it is that this need of the divine which man experiences within himself grows up into a religion, the Modernists reply thus: Science and history, they say, are confined within two limits, the one external, namely, the visible world, the other internal, which is consciousness. When one or other of these boundaries has been reached, there can be no further progress, for beyond is the unknowable. In presence of this unknowable, whether it is outside man and beyond the visible world of nature, or lies hidden within in the subconsciousness, the need of the divine, according to the principles of Fideism, excites in a soul with a propensity towards religion a certain special sentiment, without any previous advertence of the mind: and this sentiment possesses, implied within itself both as its own object and as its intrinsic cause, the reality of the divine, and in a way unites man with God. It is this sentiment to which Modernists give the name of faith, and this it is which they consider the beginning of religion.
8. But we have not yet come to the end of their philosophy, or, to speak more accurately, their folly. For Modernism finds in this sentiment not faith only, but with and in faith, as they understand it, revelation, they say, abides. For what more can one require for revelation? Is not that religious sentiment which is perceptible in the consciousness revelation, or at least the beginning of revelation? Nay, is not God Himself, as He manifests Himself to the soul, indistinctly it is true, in this same religious sense, revelation? And they add: Since God is both the object and the cause of faith, this revelation is at the same time of God and from God; that is, God is both the revealer and the revealed.
Hence, Venerable Brethren, springs that ridiculous proposition of the Modernists, that every religion, according to the different aspect under which it is viewed, must be considered as both natural and supernatural. Hence it is that they make consciousness and revelation synonymous. Hence the law, according to which religious consciousness is given as the universal rule, to be put on an equal footing with revelation, and to which all must submit, even the supreme authority of the Church, whether in its teaching capacity, or in that of legislator in the province of sacred liturgy or discipline.