On December 18th. 1886, a young man of seventeen years of age noted in his diary: „(On Pöstlingerberg hill) Cloudless sky above me, clad in reddish gold by the setting evening sun, before me the freshly snow covered peaks of the extended alpine chain in its overwhelming beauty and the pine forest-verdant, familiar rear view of the ridge of hills surrounding the city, then far off in the distance the boundless plain in its azure hues […] As if with irresistible force, my train of thought tore itself away from the narrow bonds of sensuality: my entire being and thinking steeped itself to the point of self-forgetfulness in the eternal, omnipresent thought of the Godhead. In unsuspected brightness, an idea, which for years had been lost, flashed back into my mind, an idea of the Godhead, eternity and human dignity.“
This experience on the familiar landmark peak overlooking Linz (Upper Austria) left an indelible mark on the whole life of the philosopher Robert Reininger. Out of it sprang the realization of his true vocation, namely to impart this great secret to mankind with the aid of his philosophical talent. Over the decades of his teaching career at Vienna University (1913 - February 1940) he was constantly at pains to point out in lectures the one and only reality, the „primal experience“ in which everything now always is, and to contrast this with the world of the „I“, which we create through reflection, through our conventional thinking and ultimately through language. In the Indian Upanishads and in the writings of H.P.Blavatsky, Meister Eckhart and Goethe but also in Schopenhauer and Nietzsche he came across a similar realization. Reininger also calls the „primal experience“ „primary ego“ or „intelligible ego“ - following the lead of Immanuel Kant, whom he esteemed, though Reininger in actuality saw himself only as „partially Kantian“.
On September 22nd., 1918 he noted: „The intelligible I cannot itself be regarded as a product of this development but must rather be thought of as timelessly being, and its ‚evolution‘ can only be thought of as a gradual breaking through of light through darkness: the intelligible I does not become but rather simply discovers itself! And it grows out of the empirical [I], so to speak, and through its ethical confirmation.“ 
Philosophy on the Foundation of Mystical Experience
In conspicuous contrast to his Viennese colleagues, Reininger also held lectures on Indian philosophy. Himself impressed by the Buddhist ethic of compassion, particularly as regards benevolence to animals, he was also greatly interested in the Atman-Brahman doctrine of the ancient Indian Upanishads.
Proceeding from his mystical experience, he attempted to develop a philosophy which by necessity bore the stamp of the mind. To be sure, he followed the lead of philosophers like Spinoza, Fichte, Schopenhauer and Nietzsche. He also sought compromise, however, with the „empiricists“ and „positivists“ such as the founder of the „Viennese Circle“ Moritz Scheck, one of his colleagues at the University.
In Reininger’s philosophical conception it becomes clear that integrating a religious experience into classical European philosophizing cannot normally succeed, since logic cannot be derived from mysticism. Mysticism can be a starting point or an embedding for rationality - as in Spinoza - but intellectual knowledge is a different domain from wisdom. The mind is useful and important but has its limitations. Only with the help of intuition, a „thinking from the heart“, can the gap be bridged. This type of „thinking“ is a comprehensive understanding, a spontaneous conceiving of that which is.
As mentioned above, Reininger greatly valued the philosophy of the Netherlands philosopher Baruch de Spinoza. The latter had derived his system from the basic tenet that God exists and that Nature is one with God, i.e. that there is nothing but God. Through increasing insight, Man is thus deemed able to purify his mind from its usual entanglement through mere opinion and, with the aid of true intuition, to grow towards all-embracing Divine love and ultimately comprehend everything.
What is real? What is true?
Reininger, too, reserved pride of place in his teaching for primal experience. From this, the world is believed to develop in a rational gradation of ever loftier realizations, all of which, however, represent only relative truths and are constantly „superseded“ from a higher point of view. Each „truth“ is thus initially „absolute“ but soon becomes relative. Reininger denied absolute truth as such. In the phenomenal world, only relative truths exist, which originate through language, whereas primal experience is not „true“ but „real“. The reality of the world does not equate with the reality of primal experience.
In fact, we’re usually firmly convinced that we and the world are „real“ and that we know what is „true“ and what is „real“. We correct „false“ statements or judgments and speak of “errors“. We believe we can exactly specify what reality is, and what it is not, like, for example, fantasies or dreams. People who „live in their own world“ do not live in „reality“. They suffer from „loss of reality“ - a common diagnosis for the demented or psychologically ill. Actually, each and every I has its own world and reality. Often the definition of truth and reality is simply a matter of power. It is a game of illusions, Maya. It cannot be otherwise, because the I itself is only illusion.
We do not know reality. We constantly invent new truths and tinker undeterred at a supposedly ever securer receptacle for our reality. But we desire absolute truth and absolute reality! The I is, however, unable to find this, as absolute truth and absolute reality are something completely different, something which dwells in the heart and is the cause of our yearning for the eternal.
The Primary and Secondary I
For Reininger, primal experience is the awareness that accompanies all conscious experiences but is empty of content; it is the „primary I“. The „secondary I“ is the person, who through mental images (including those of one’s own physical form) perceives the world and itself as identical. This is only possible via a particular phenomenon which Reininger terms „transcendental sensation“, which constitutes the bridge to primal experience. This special pure sensation is different from physiological sensation. Through it alone can we experience „one-ness“.
According to Reininger, the person who lives from this primal experience is the auto-autonomous person, who requires no special ethic. He carries „nobility“ within himself and can always say „yes“ to existence in the present, because he is acquainted with the true self.
Among other things, he was concerned with the question of how the illusion of the world’s reality originated, namely in the sense that we believe it to be real. This leads to such considerations as: how did the two originate from the one, or how did multiplicity originate from the one, and is multiplicity identical with one-ness or something different? Or: Is the „Fall“ a falling from paradise into another, rejected, wicked world or is experiencing reality of the (secondary) I just a dream from which we must awaken, in order to recognize that we are actually divine and one?
Metaphysics of Silence
Reininger found no answer to this question and ended up with a „metaphysics of silence“, i.e. metaphysics must limit itself to „pointing out the place where the final and most profound secret is hidden: in the primal experiencing of the Now. […] Philosophy ends in astonishment, it remains the metaphysical feeling of the secret. The boundaries of rational cognition cannot be broken through!“  „Metaphysical Man is deeply and constantly conscious of the profoundest mystery, which each moment of experience conceals within itself. He lives in the certainty of standing in the eternal while in the midst of the temporal.“ For Reininger, this was literally metaphysical experience.
In the human heart, as the Rosicrucians teach, slumbers an element, through which metaphysical experiences become possible. They call it the „primal atom“, the „rose-bud“. When it awakens, consciousness of fundamental oneness is born. In the beginning it can germinate like a delicate, light shimmer and in the course of life blossom forth into a „fragrant rose“; or else, in „primal experience“, a person suddenly becomes fully aware of his divine descent. That gift of grace was bestowed upon Robert Reininger, who to the end of his life knew that he was sustained by it and utilized his intelligence and talents to serve humanity with this message.
 1 Nawratil, Karl (1969): Robert Reininger. Leben – Wirken – Persönlichkeit, Wien: Verlag der Österreichischen Akademie der Wissenschaften (=Philosophisch-historische Klasse, Sitzungsberichte, 265. Bd.), p. 36
 Nawratil, Karl (Hrsg.) (1974), Robert Reininger. Jugendschriften 1885 – 1895 und Aphorismen 1894 – 1948, Wien: Verlag der Österreichischen Akademie der Wissenschaften (= Philosophisch-historische Klasse, Sitzungsberichte, 296. Bd.), p. 186
 Reininger, Robert (1948): Metaphysik der Wirklichkeit. Zweite, gänzlich neubearbeitete Auflage, Wien: Braumüller, 2 Bde., Vol.2, p.214