In its essence, Brunner's thought is holist. It proceeds from the assumption of the oneness of all being. In scientific terms, this unity is manifest in the universal complex of causal relationships.

Brunner put forward a doctrine of three modes of thought. First, practical understanding comprises those mental activities which contribute toward the maintenance of our physical well-being. This includes scientific knowledge. When we reflect scientifically on the world around us, we ultimately perceive that it consists of a complex of causally-related phenomena. This is the sense in which Brunner speaks of "The One".

Brunner asserts that by modifying our practical understanding to include this fact of absolute unity, we can significantly improve our practical understanding, and hence the quality of our lives. This contextualizing of our lives within absolute unity Brunner calls spiritual thought. Brunner maintains, however, that few people are interested in any such modification because it means relativizing our own egos and interests. Instead, most people seek to absolutize their egos and interests, a mode of false thinking that Brunner calls superstition.

Each of the three modes of thought consists of three specificates. In the practical understanding, the specificates are feeling, knowing and willing. In spiritual life, these specificates are modified to become, respectively, art, philosophy and mysticism (love). Superstition distorts the specificates of spiritual life, transforming them into religion, metaphysics and moralism.

Feeling, knowing and willing are the terms that Brunner uses for the specificates of the practical understanding. In information theory, these can be understood as input, processing, and output. In psychology they can be designated affectivity, cognition and volition.

Brunner and Judaism

The opposition between the spiritual and the religious is a major theme in Brunner's work. He contends that Judaism is essentially anti-religious, and culminates his argument with his own translation of the Shema Yisrael: "Hear O Israel, Being is our god, Being is one". He juxtaposes priestly and rabbinical to prophetic Judaism, wherein the latter represents the true mystical essence in opposition to the former which represent superstition.

Brunner and Christianity

For Brunner, Christ represents the greatest representative of what he calls "die Geistigen". The English translation of this term is hotly debated among Brunnerians. In Our Christ it is given as "the spiritual elite." This spiritual elite is contrasted with what Brunner calls "das Volk", who constitute the vast majority of mankind. Brunner's doctrine of the spiritual elite is essentially a doctrine of genius. Thus he argues that Christ is the greatest of geniuses. Brunner relies heavily on Spinoza in all matters, including Christology.

Brunner argues that Christ's conception of what he calls "the Father" corresponds to what Brunner calls "das Denkende". The translation of this term is also debated. In Our Christ it is rendered as "the Cogitant". It corresponds to the formless, imageless essence of being which we attain to through mystical apperception. The spiritual elite are those who have a clear apperception of this essence. Most people have little or no ability or desire to work toward this clarity, adhering instead to a view of the absolute based on their sense impressions. For Brunner, Judaism is an anti-religion, a protest against religion with its absolutizing of the relative. Christ is the purest example of this protest, living as he did completely within the clarity of his mystical apperception.

Brunner contextualizes Christ's execution in his doctrine of genius by showing how the leaders of the people have consistently acted throughout history to silence geniuses. Brunner expresses the hope that his doctrine, by making explicit the distinction between geniuses and common people, will at last end the war between them. Geniuses will stop trying to turn common people into geniuses, and common people will stop trying to turn geniuses into common people.

This doctrine of the spiritual elite and the people is radically at odds with contemporary egalitarianism. It is a matter of ongoing debate among Brunnerians how to deal with this. It is clear that Brunner put it forward as a "constructive fiction" which would underlie the human sciences just as the constructive fiction of an indivisible particle underlies physics and chemistry. Brunner's doctrine of the spiritual elite and the people does assist to explain some previously inexplicable social and psychological phenomena, Christ not least.

As for the Christian religion, Brunner sees it as a process of distortion by which Christ becomes de-Judaized and divinized through the massive influx of Gentiles. Finally, he calls for Jews to reclaim Christ as their own highest exemplar.

Brunner and Israel

Throughout his life, Brunner was anti-Zionist, although there is evidence that he was reconsidering his opposition to the founding of an Israeli state toward the end of his life in light of events in Europe. (see Assimilation und Nationalismus: ein Brefwechsel mit Constantin Brunner / Willy Aron).

The spiritual elite

Brunner's essential aim was to found a community of spiritually-minded people. He left the practical questions relating to this project deliberately unanswered. His devotees continue to puzzle over how to carry out this goal.

Influence and relevance

Brunner was once described as "one of the more important figures" in Europe along with Max Reinhardt, Gerhart Hauptmann, Maximilian Harden, Richard Wagner, and Leo Tolstoy (Confessions of a European Intellectual / Franz Schoenberner). He corresponded with Walther Rathenau, Martin Buber, Gustav Landauer and Lou Andreas-Salome. Albert Einstein read Brunner and, while appreciating his critical insight and sharing his devotion to Spinoza, rejected his philosophy, particularly where it stood opposed to Kant (see Einstein-Aron correspondence, Albert Einstein Archives, Hebrew University in Jerusalem).

With the Second World War, Brunner's books were burned and his devotees scattered. Post-war conditions did not immediately favour a revival of interest, despite the efforts of such a luminary as Yehudi Menuhin. There is still some interest, as an Internet search will show. Nevertheless, it is strange that Brunner's book on Christ is almost nowhere mentioned in any of the discussion relating to the historical Jesus.