Early in the 20th century, many scholars, intellectuals, and philosophers looked on the relationship of religion, philosophy, and science as an evolutionary one in which the more sophisticated ways of looking at the world simply replaced the older ways. Religion itself was often thought to arise from magic, and so schemes illustrating the development of human thought might look like this:
Only science, mathematics, and logic would deserve to continue. Since these scholars thought of magic as a set of naive beliefs about how to manipulate nature, they thought that science ultimately fulfilled this promise by actually manipulating nature in the ways that magic had promised. Especially associated with this evolutionary scheme was James George Frazer, whose classic The Golden Bough [1890, 1900, 1906-1915] was an extended argument and illustration of it.
This all, of course, dismissed any other possible contents of religion or philosophy as so much window dressing or misdirection. Some philosophers have simply decided that philosophy also should simply end (e.g. Karl Marx, Richard Rorty). Others found some inoffensive thing for philosophy to do, like clarify language, or identify itself with logic (e.g. Logical Positivism, Ludwig Wittgenstein).
While plenty of intellectuals retain a broad hostility towards religion, this kind of evolutionary scheme is now generally discredited in actual philosophy or history of religion scholarship. Ancient religions did not grow out of magic, and science does not address many, or most, of the concerns that have actually been central in traditional religion and philosophy. It is possible to go to the opposite extreme and reject any evolutionary sense of the development of human thought, saying that all forms of thought, in all places and at all times, are simply different; but this does not address the dynamic of real changes that take place in the same places and to the same traditions. It is not much of a leap to say that those traditions, in their later forms involve levels of sophistication above what occurred earlier.
If we can see philosophy growing out of mythic thought in Greek history, the difficulty arises about just how we are to then distinguish philosophy from religion, as the two later coexist but are distinguished from each other. Socrates talks about the gods all the time, and it is not clear why he should not be regarded as a religious figure rather than a secular philosopher. As it happens, the relatively easy distinction between religion and philosophy in Western history occurs because of the historical accident that the religion of people like Socrates and Plato later ceased to exist. The old gods of the Greeks, Egyptian, Babylonians, Phoenicians, Romans, Celts, Germans, Slavs, etc. were later entirely replaced by one old religion, Judaism, and two new ones from the same tradition, Christianity and Islam. It is now possible to say "religion" and mean one of those and to say "philosophy" and simply mean "that Greek stuff" (falsafah in Arabic), where the religious side of Greek thought just need not be taken seriously.
The historical circumstances that allow for that simple pattern of distinction does not occur in India or China. A book like the Bhagavad Gita is a profoundly important religious document for Hinduism, yet it is also one of the fundamental documents of Indian philosophy. Indeed, the Gita appears to have been produced by Indian philosophy, the Sankhya and Yoga Schools, then been transformed into a religious document, and finally used for both religious and philosophical (by Vedânta) purposes later on. This kind of thing makes distinctions between religion and philosophy very difficult in the Indian tradition.
Similar difficulties exist for Chinese thought but also for Mediaeval Western thought, where philosophers are easily classified as Christian, Jewish, or Moslem. If philosophy had nothing to do with religion, then presumably it would be superfluous to identify Moses Maimonides (1135-1204) as Jewish or Avicenna (Ibn Sina, 980-1037) as Moslem. It is not, and this was a question that many such philosophers had to face at the time. The way that one of the greatest Christian philosophers, St. Thomas Aquinas (1224-1274), dealt with it was to identify different sources of authority: he distinguished "natural theology," which is based on reason alone, from "dogmatic theology," which is based on revelation. Jewish and Moslem philosophers had made similar distinctions, and some of them had even thought, which St. Thomas didn't, that reason could ultimately justify everything in religion.
Definitions for religion and philosophy must involve similar distinctions, where the original context of all thought is mythic. Since myth does not argue, but philosophy does, a rule of thumb for religion is that it mixes in philosophic elements but always retains an authoritative link to a mythic context. The most important thing about that mythic context, however, is not always that it exerts a dogmatic authority, but that it is historical. Philosophy cannot conjure up historical particulars out of pure reason, but religion always relates its truth to historical particulars, the actual source of the religion or its received tradition. Furthermore, contrary to the earlier evolutionary schemes about human thought, it must be accepted that mythic thought, and so religion, cannot be replaced by philosophy, or by science. An evolutionary pattern thus could look like this:
The only ongoing traditions whose worth we might fundamentally question would be those of magic, astrology, and other occult "arts," although there is no doubt that serious forms of some of these continue to exist. None of the traditions really continue independently after their origin. Religion, philosophy, and even science exert influences on each other. Only theology and philosophy are shown connected below their origins because it is hard to know what to call someone like St. Thomas Aquinas, primarily a philosopher or primarily a theologian.What philosophy contains that science cannot are real questions about Being and Value. Science must assume the reality of its objects, so it cannot have a critical metaphysical attitude; nor can it make any judgments at all about value, since some principles of value must be assumed in order to judge in some predictive or experimental way the value consequences of a scientific theory. What religion contains that philosophy cannot is the actual value embodied in large interpretative structures concerning life, the world, etc.: philosophy is only descriptive and has difficulty justifying any first principles that it might identify. Where Aristotle and mediaeval philosophy relied on self-evident principles, recent philosophers often assume an attitude of "this is the way we are going to do it" (Cf. A.J. Ayer, Language, Truth and Logic). That neither justifies nor even persuades; but such talk continues in the language of philosophers like Richard Rorty ("deconstructionism" or "post-modernism"), that "truth" consists of the "decisions that we make." Why you and I should care about the "decisions" that Rorty makes is a good question.
Philosophy of Religion