The Traditionalist School of thought (not to be confused with Traditionalist Catholicism, and also known as perennialism, the perennial philosophy, or Sophia Perennis), attained its current form with the French metaphysician René Guénon, although its precepts are considered by adherents to be timeless and to be found in all authentic traditions. The term Philosophia Perennis goes back to the Renaissance, while the ancient Hindu expression Sanatana Dharma - Eternal Truth - has much the same signification.
The other founding figures of the Traditionalist School were the German-Swiss philosopher Frithjof Schuon and the Ceylonese scholar Ananda Coomaraswamy. To these were added over time such figures as Titus Burckhardt, Martin Lings, and Seyyed Hossein Nasr.
 Tradition and religious pluralism
Rejecting the idea of progress and the enlightenment paradigm, Perennialist authors describe modern civilization as a pseudo and decadent civilization, which manifests the lowest possibilities of the Kali Yuga (the Dark Age of the Hindu cosmology). To the “modern error,” the Perennialists oppose an everlasting wisdom of divine origin, “a Primordial Tradition”, transmitted from the very origin of humanity and partially restored by each genuine founder of a new religion. Perennialists have a very specific definition of “Tradition.” Tradition implies the idea of a transmission (tradere), but for Guénon and his followers, tradition does not have a human origin and may be considered as principles revealed from Heaven and binding man to his divine origin. Beyond the diversity of religious forms, they discern a single Tradition (with a capital letter), what Schuon called a “transcendent unity”. They claim that the historically separated traditions share not only the same divine origin but are based on the same metaphysical principles, sometimes called philosophia perennis.
So far as can be discovered, the term “philosophia perennis” is modern, first appearing in the Renaissance. Though the term “philosophia perennis” is widely associated with the philosopher Leibniz who himself owes it to the sixteenth century theologian Augustinus Steuchius. But the ideal of such a philosophy is much older and one could easily recognize it in the Golden Chain (seira) of Neoplatonism, in the Patristic Lex primordialis, in the Islamic Din al- Fitra or even in the Hindu Sanathana Dharma.
 The rediscovery of the Sophia Perennis
The French author, René Guénon (1886-1951) was in a certain sense a pioneer in the rediscovery of this Philosophia Perennis or better Sophia Perennis in the 20th century. His view largely shared with later Perennialist authorities, is that Semitic religions have an exoteric/esoteric structure. Exoterism, the outward dimension of religion, is constituted by religious rites and a moral but also a dogmatic theology. The exoteric point of view is characterized by its “sentimentalist”, rather than purely intellectual nature and remains fairly limited. Based on the doctrine of creation and the subsequent duality between God and creation, exoterism does not offer means to transcend the limitations of the human state. The goal is only religious salvation that Guénon defines as a perpetual state of beatitude in a celestial paradise. In the Traditionalist view, esoterism is more than the complement of exoterism, the spirit as opposed to the letter, the kernel with respect to the shell. Esoterism has at least de jure, a total autonomy with respect to religion for its innermost substance is the Primordial Tradition itself. Based on pure metaphysics -by which Guénon means a supra-rational knowledge of the Divine, a gnosis, and not a rationalist system or theological dogma- its goal is the realization of the superior states of being and finally the union between the individual self and the Principle. Guénon calls this union “the Supreme Identity”.
By Principle, Guénon and Schuon means more than the personal God of exoteric theology: the suprapersonal Essence, the Beyond-Being, the Absolute both totally transcendent and immanent to the manifestation. In their view the innermost essence of the individual being is non-different from the Absolute itself. Guénon refers here to the Vedantic concepts of Brahman (Principle), Atma (Self) and Moksa (Deliverance). This reference is not accidental or circumstantial. For Guénon, the Hindu Sanathana Dharma represents in fact “the more direct heritage of the Primordial Tradition”. More generally, the great traditions of Asia (Advaita Vedanta, Taoism and Mahayana Buddhism) play a paradigmatic function in his writings. He considers them as the more rigorous expression of pure metaphysics, this supra-formal and universal wisdom being nevertheless in itself neither eastern nor western.
Contrary to the Semitic religions, those Asian religions don’t have an esoterism/exoterism structure which has emerged only later in the historical cycle, at a time of growing spiritual decadence, where the vast majority of the people were no longer “qualified” to understand metaphysical truths and transcendent possibilities of the human state.
 The criticism of modernity
For Guénon, the author of the Crisis of the Modern World, the end of this descending process is modernity itself, which manifests the lowest possibilities of the Kali Yuga. Guénon also called our age the Reign of the Quantity, because man and the cosmos are more and more determined, ontologically speaking, by matter. The tragedy of the Western world since the Renaissance is, in his view, that it has lost almost any contact with the Sophia Perennis and the Sacred. Consequently, in the Western context, it is virtually impossible for a spiritual seeker to receive a valid initiation and to follow an esoteric path.
It is important to mention here that although Guénon has influenced a figure such as Julius Evola, none of the main traditionalist authors have shared Evola's political views. As a matter of fact, his writings are commonly seen in most traditionalist circles as an anti-traditional deviation, based on an inversion of the hierarchy between contemplation and action. Traditionalists authors were rather apolitical, although conservatively-inclined, avoiding any political activity.
 The initiatory path
Although, he has pleaded in his first books for a restoration of traditional “intellectualité” in the West on the basis of Roman Catholicism and Freemasonry, it is clear that Guénon, very early on, gave up the idea of a spiritual resurrection of the West on a purely Christian basis. Having denounced the lure of Theosophism and neo-occultism, two influential movements that were flourishing in his lifetime, Guénon was initiated in 1912 in the Shadhili order and moved to Cairo in 1930 where he spent the rest of his life as a Sufi Muslim. To his many corresponds, he clearly designated Sufism as the more accessible form of traditional initiation for Westerns eager to find what does not exist any more in the West: an initiatory path of knowledge (Jnana or Gnosis), comparable to Advaita.
As a matter of fact, although Ananda Coomaraswamy was an Hindu, many followers of Guénon such as Frithjof Schuon, Martin Lings, Titus Burckhardt have been initiated into Sufism. Others remain Christians such as the religious philosopher Jean Borella. Marco Pallis was a Buddhist. The most influential representatives of this school in Northern Europe are all Muslim converts: Kurt Almqvist, Tage Lindbom and Ashk Dahlén.
 Academic influence
It could be argued that Traditionalism has a strong, although discrete impact in the field of Comparative Religion and particularly on the young Mircea Eliade, although he was not himself a member of this school. Contemporary scholars such as Huston Smith, William Chittick, Harry Oldmeadow, James Cutsinger and Seyyed Hossein Nasr have advocated Perennialism as an alternative to secularist approach to religious phenomena.