Here is the Catholic Encyclopedia:
The term given, in general, to all those theories, which, for one reason or another, deny that it is the duty of man to worship God by believing and practicing the one true religion.
This is religious indifferentism, condemned by the Church and refers to the fact that the Catholic Faith is the one, true Faith.
Then, there is political indifferentism, which does not acknowledge a hierarchy of religions.
This religious Indifferentism is to be distinguished from political indifferentism, which is applied to the policy of a state that treats all the religions within its borders as being on an equal footing before the law of the country. Indifferentism is not to be confounded with religious indifference. The former is primarily a theory disparaging the value of religion; the latter term designates the conduct of those who, whether they do or do not believe in the necessity and utility of religion, do in fact neglect to fulfil its duties.
The CE goes on to define terms exactly. For example, dualistic materialism-Marxism-is a type of absolute indifferentism. Any belief which denies the final goal of man as spiritual and which denigrates individualism is a type of absolute indifferentism.
Absolute indifferentism
Under the above general definition come those philosophic systems which reject the ultimate foundation of all religion, that is,man's acknowledgment of his dependence on a personal creator, whom, in consequence of this dependence, he is bound to reverence, obey, and love. This error is common to all atheistic, materialistic, pantheistic, and agnostic philosophies. If there is no God, as the Atheist professes to believe, or if God be but the sum of material forces, or if the Supreme Being is an all-embracing, all-confounding totality in which human individuality is lost, then the personal relationship in which religion takes its rise does not exist. Again, if the human mind is incapable of attaining certitude as to whether God exists or not, or is even unable to form any valid idea of God, it follows that religious worship is a mere futility. This error is shared also by the Deists, who, while they admit the existence of a personal God, deny that he demands any worship from His creatures. These systems are answered by the apologist who proves that every one is bound to practice religion as a duty towards God, and in order that he may attain the end for which he has been called into existence.Again, here is expanded definition of the type which states all religions are the same.
Restricted indifferentism
In distinction from this absolute Indifferentism, a restricted form of the error admits the necessity of religion on account, chiefly, of its salutary influence on human life. But it holds that all religions are equally worthy and profitable to man, and equally pleasing to God. The classic advocate of this theory is Rousseau, who maintains, in his "Emile", that God looks only to the sincerity of intention, and that everybody can serve Him by remaining in the religion in which he has been brought up, or by changing it at will for any other that pleases him more (Emile, III). This doctrine is widely advocated today on the grounds that, beyond thetruth of God's existence, we can attain to no certain religious knowledge; and that, since God has left us thus in uncertainty, He will be pleased with whatever form of worship we sincerely offer Him. The full reply to this error consists in the proof that Godhas vouchsafed to man a supernatural revelation, embodying a definite religion, which He desires that all should embrace and practice. Without appealing to this fact, however, a little consideration suffices to lay bare the inherent absurdity of thisdoctrine. All religions, indeed, may be said to contain some measure of truth; and God may accept the imperfect worship ofignorant sincerity. But it is injurious to God, Who is truth itself, to assert that truth and falsehood are indifferent in His sight. Since various religions are in disagreement, it follows that, wherever they conflict, if one possesses the truth the others are inerror. The constituent elements of a religion are beliefs to be held by the intellect, precepts to be observed, and a form ofworship to be practiced. Now — to confine ourselves to the great religions of the world — Judaism, Mohammedanism,Christianity, and the religions of India and the Orient are in direct antagonism by their respective creeds, moral codes, and cults. To say that all these irreconcilable beliefs and cults are equally pleasing to God is to say that the Divine Being has no predilection for truth over error; that the true and the false are alike congenial to His nature. Again, to hold that truth andfalsehood equally satisfy and perfect the human intellect is to deny that reason has a native bent towards, and affinity for,truth. If we deny this we deny that any trust is to be placed in our reason. Turn to the ethical side of the question. Here again there is conflict over almost all the great moral issues. Let an illustration or two suffice. Mohammedanism approves polygamy,Christianity uncompromisingly condemns it as immoral. If these two teachers are equally trustworthy guides of life, then there is no such thing as fixed moral values at all. If the obscene orgies of phallic worship are as pure in the sight of God as the austere worship that was conducted in the temple of Jerusalem, then we must hold the Deity to be destitute of all moral attributes, in which case there would be no grounds for religion at all. The fact is that this type of Indifferentism, though verbally acknowledging the excellence and utility of religion, nevertheless, when pressed by logic, recoils into absolute Indifferentism. "All religions are equally good" comes to mean, at bottom, that religion is good for nothing.Another take on indifferentism is explained here. The long explanation is worth reading. Freemasonry falls into the first two categories and Anglicanism falls into this third one.
Liberal or latitudinarian indifferentism
Origin and growth
The foregoing types of Indifferentism are conveniently called infidel, to distinguish them from a third, which, while acknowledging the unique Divine origin and character of Christianity, and its consequent immeasurable superiority over all rival religions, holds that what particular Christian Church or sect one belongs to is an indifferent matter; all forms of Christianity are on the same footing, all are equally pleasing to God and serviceable to man. On approaching this third error one may advantageously inquire into the genesis of Indifferentism in general. In doing so we shall find that liberal Indifferentism, as the third type is called, although it arises in belief, is closely akin to that of infidelity; and this community of origin will account for the tendency which is today working towards the union of both in a common mire of scepticism. Indifferentism springs from Rationalism. By Rationalism here we understand the principle that reason is the sole judge and discoverer of religious truth as of all other kinds of truth. It is the antithesis of the principle of authority which asserts that God, by a supernatural revelation, has taught man religious truths that are inaccessible to our mere unaided reason, as well as other truths which, though not absolutely beyond the native powers of reason, yet could not by reason alone be brought home to the generality of men with the facility, certitude, and freedom fromerror required for the right ordering of life. From the earliest ages of the Church the rationalistic spirit manifested itself in various heresies. During the Middle Ages it infected the teachings of many notable philosophers and theologians of the schools, and reigned unchecked in the Moorish centres of learning. Its influence may be traced through the Renaissance to the rise of theReformation (see RATIONALISM).From the beginning of the Reformation the rationalistic current flowed with ever-increasing volume through two distinct channels, which, though rising apart, have been gradually approaching each other. The one operated through purely philosophic thought which, wherever it set itself free from the authority of the Church, has on the whole served to display what has been justlycalled the "all-corroding, all-dissolving scepticism of the intellect in religious matters". Rationalistic speculation gave rise successively to the English Deism of the eighteenth century, to the school of the French Encyclopaedists and their descendants, and to the various German systems of anti-Christian thought. It has culminated in the prevalent materialistic, monistic, andagnostic philosophies of today. When the Reformers rejected the dogmatic authority of the living Church they substituted for it that of the Bible. But their rule of faith was the Bible, interpreted by private judgment. This doctrine introduced the principle ofRationalism into the very structure of Protestantism. The history of that movement is a record of continually increasing divisions, multiplications of sects, with a steady tendency to reduce the contents of a fixed dogmatic creed. In a few words Cardinal Newman has summed up the lesson of that history: "Experience proves surely that the Bible does not answer a purpose for which it was never intended. It may be accidentally the means of converting individuals; but a book after all cannot make a stand against the wild living intellect of man, and in this day it begins to testify, as regards its own structure and contents, to the power of that universal solvent which is so successfully acting upon religious establishments" (Apologia pro Vita Sua, London, 1883, v. 245). As divisions increased in the general body of Protestantism, and as domestic dissensions arose in the bosom of particular denominations, some of the leaders endeavoured to find a principle of harmony in the theory that the essential doctrines of Christianity are summed up in a few great, simple truths which are clearly expressed in Scripture, and that, consequently, whoever believes these and regulates his life accordingly is a true follower of Christ. This movement failed to stay the process of disintegration, and powerfully promoted the opinion that, provided one accepts Christianity as the true religion, it makes little difference to what particular denomination one adheres. The view spread that there is no creed definitely set forth in Scripture, therefore all are of equal value, and all profitable to salvation. Large numbers in the Church of England adopted this opinion, which came to be known as Liberalism or Latitudinarianism. It was not, however, confined to one form of Protestantism, but obtained adherents in almost every body inheriting from the Reformation. The effort was made to reconcile it with the official confessions by introducing the policy of permitting every one to interpret the compulsory formulae in his own sense.
Indifferentism, liberal and infidel, has been vigorously promoted during the past half century by the dominance of Rationalism in all the lines of scientific inquiry which touch upon religion. The theory of evolution applied to the origin of man, Biblical criticism of the Old and New Testament, the comparative study of religions, archaeology, and ethnology, in the hands of men who assume as their primary postulate that there is no supernatural, and that all religions, Christianity included, are but the offspring of the feeling and thought of the natural man, have propagated a general atmosphere of doubt or positive unbelief. As a result, large numbers of Protestants have abandoned all distinctly Christian belief, while others, still clinging to the name, have emptied their creed of all its essential dogmatic contents. The doctrine of Scriptural inspiration and inerrancy is all but universally abandoned. It would not, perhaps, be incorrect to say that the prevalent view today is that Christ taught no dogmatic doctrine, His teaching was purely ethical, and its only permanent and valuable content is summed up in the Fatherhood of God and the brotherhood of man. When this point is reached the Indifferentism which arose in belief joins hands with the Indifferentism of infidelity. The latter substitutes for religion, the former advocates as the only essential of religion, the broad fundamental principles of natural morality, such as justice, veracity, and benevolence that takes concrete form in social service. In some minds this theory of life is combined with Agnosticism, in others with a vague Theism, while in many it is still united with some vestiges of the Christian Faith.
Along with the intellectual cause just noted, another has been what one might call the automatic influence proceeding from the existence of many religions side by side in the same country. This condition has given rise to the political indifferentism referred to in the opening of this article. Where this state of affairs prevails, when men of various creeds meet one another in political, commercial, and social life, in order that they may carry on their relations harmoniously they will not demand any special recognition of their own respective denominations. Personal intercourse fosters the spirit of tolerance, and whoever does not unflinchingly hold to the truth that there is but one true religion is apt to be guided in his judgments by the maxim, "From their fruits ye shall know them." On observing that probity and good intention mark the lives of some of his associates who differ in their religious beliefs, he may easily come to the conclusion that one religion is as good as another. Probably, however, many who speak thus would acknowledge the fallacy of this view if pushed by argument. On the other hand, great numbers of theoretical Indifferentists display unmistakable hostility to the Catholic Church; while, again, persons devoid of all religious belief, favour the Church as an efficient element of police for the preservation of the social order.
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