Because religious ideas that are obscure or cryptic may be called “mystical” in popular parlance, mysticism is often mistakenly thought to be essentially irrational. Although much mysticism, like much religion, is indeed irrational, other mystical traditions take pride in their adherence to reason.

In the West, Diogenes of Apollonia, a Greek philosopher of the 5th century bce, introduced mystical ideas into Greek philosophy. Diogenes maintained that “all existing things are created by the alteration of the same thing, and are the same thing.” This one ultimate substance, according to Diogenes, has nous (“mind” or “intellect”) and “is called Air.” All humans and animals breath Air, which “for them is both Soul (Life) and Intelligence.” In his Nicomachean Ethics, the Greek philosopher Aristotle stated that the contemplative life consists of the soul’s participation in the eternal through a union between the soul’s rational faculty and the nous that imparts intelligibility to the cosmos.

For more than 2,000 years, Western rational mystics have contemplated nature—its forms, structures, laws, and quantities—as a means of participating in the divine intellect. While some rational mystics have regarded nature as a contemplative end in itself, for others the contemplation of nature is a source of insight regarding its creator. The most famous modern representative of this tradition of rational mysticism is the German-born physicist Albert Einstein, who wrote in the collection Living Philosophies (1931):

The most beautiful and profound emotion we can experience is the sensation of the mystical. It is the sower of all true art and science. He to whom this emotion is a stranger … is as good as dead. To know that what is impenetrable to us really exists, manifesting itself as the highest wisdom and the most radiant beauty, which our dull faculties can comprehend only in their most primitive forms—this knowledge, this feeling, is at the center of true religiousness.

The accord of mysticism with reason is also an age-old tradition in China. In the Analects the philosopher and bureaucrat Confucius (551–479 bce) advocated ethical integrity as a code of conduct for gentlemen of the Chinese ruling class. He claimed that ethics is the natural basis of government, as is proved pragmatically by the efficiency of ethical governance. The ethical life is the natural way (Dao) toward sociopolitical effectiveness. The Confucian program of self-improvement was explicitly understood to include a meditative practice by the philosopher Xunzi (born c. 300 bce), who wrote:

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Hinduism: Mysticism

If he who seeks to abide by the Way has emptiness, then he may enter into it; if he who seeks to serve the Way has unity, then he may master it; if he who seeks to meditate on the Way has stillness, then he may perceive it. He who understands the Way and perceives its nature, he who understands the Way and carries it out, may be said to embody the Way.

Through selflessness, one might become sufficiently empty of self-interest to participate in the objective reality of the Way. This was not simply a conforming with the Way; it was a kind of uniting with it, by accepting the Way’s direction as one’s own. Once participation was achieved, unity or integrity with the Way facilitated mastery; and meditation in “stillness” permitted direct experience of the Way. It then remained only to embody the Way by acting in accordance with it.

During the Song (960–1279) and Ming (1368–1644) dynasties, when neo-Confucianism was the official philosophy of government administrators throughout imperial China, a meditative practice known as “quiet sitting” was often joined together with study to promote self-cultivation. Quiet sitting consisted of suspending thought so that objects ceased to present themselves in the mind. The remaining consciousness was interpreted as the original substance (benti) or principle (li) of the mind; but because “there is no distinction between interior and exterior,” it was simultaneously the foundation of all things. Neo-Confucian mysticism has been termed an “ethical mysticism,” but it is simultaneously a rational mysticism because it viewed ethics as the natural basis of effective sociopolitical organization.