He spent most of his academic career at the University of Tübingen, where he published work influenced by Lebensphilosophie and German Romanticism including The Spirit of Catholicism (1924), which argued for an understanding of the church as a community and for a revitalisation of Christian faith.
[5] In 1910 he published an article critical of Pius X's requirement that priests take the oath against modernism, which he described as "the official death notice regarding all Catholic scholarship" in Germany.
[9] This aspect of his work, along with his use of the German language rather than Latin and his emphasis on the humanity of Jesus, once again drew scrutiny from the Holy Office, and his book The Spirit of Catholicism (1924) was threatened with placement on the Index Librorum Prohibitorum in 1932.
[10] Adam was one of several German Catholic theologians who sought rapprochement between the church and Nazi Germany after Adolf Hitler's rise to power.
[18] Nonetheless, Adam also argued that Christians were obliged to treat Jews justly and lovingly, and that it was wrong to deny the Jewishness of Jesus.
[28][29] His aim was to encourage Catholicism to modernise by responding to the "positive" elements of Nazism, and to limit the influence of the German Faith Movement in order to prevent the disintegration of Christianity in the Nazi state.
[32][33] Bernhard Lichtenberg wrote to Adam upon reading the transcript of the lecture, accusing him of offering a "fatal vagueness" under the pretence of a clear delineation of the status of German Catholicism.
[37] Lichtenberg was later arrested, convicted of violating the Pulpit Law and the Treachery Act of 1934 and imprisoned, and died while being taken to the Dachau concentration camp.
[32] The essay argued that although Jesus was Jewish, he was not purely so, because he came from Galilee, a region where interracial marriage was common, and because the Immaculate Conception of the Virgin Mary meant he lacked the "ugly dispositions and forces which we condemn in full blooded Jews.
[45] These tendencies, Adam thought, required new social and political formations that would restore order and encourage community, tradition and Christian faith.
[46] The theologian Klaus Schatz [de] argued that Adam's "predilection for the 'vital' and 'organic'" and his rejection of rationalism and liberalism contributed to his willingness to accommodate Nazism.
[47] Spicer argues that, while Adam's overtures to Nazism were understandable in the early 1930s, by 1939, after Kristallnacht and the Nazis' persecution of the Catholic Church, they became incomprehensible.
[47] Spicer claims Adam "allowed himself to be so influenced by the National Socialist milieu that he could not properly discern between what he should accept and reject from the movement's ideology.
"[48] John Connelly argues that Adam saw Hitler as a figure capable of bridging the divide between German Catholics and Protestants, in keeping with his earlier support for ecumenism.
[40] Neither Adam nor any of Tübingen's other Catholic theologians were among those imprisoned or banned from teaching for promoting Nazism or the Nazi regime's human rights violations.
[55] In The Spirit of Catholicism (1924), Adam critiqued rationalism, which he argued had distanced people from themselves, from their communities and from God; the Enlightenment, which he claimed prioritised intellect over feelings and relationships; and modernity itself.
[11] Karl Heim, a Protestant colleague of Adam's at Tübingen, responded to The Spirit of Catholicism with a series of lectures that were published under the title The Nature of Protestantism in 1925.
[60] The Spirit of Catholicism has been translated into 13 languages, and was an influence on thinkers including Robert McAfee Brown, Dorothy Day, Thomas Merton, Flannery O'Connor, Alec Vidler, Evelyn Underhill and Pope Paul VI, who drew on it in his papal encyclical Ecclesiam suam.
[65] Flannery O'Connor, in her review published in 1958, identified The Christ of Faith as containing an implicit argument against efforts to reconstruct Christianity as a syncretic religion, praised the book's critique of "the errors of liberal theology", and described it as "a master work by one of the Church's greatest living theologians.
[61] Krieg argues that Adam played a significant role in the renewal of Catholic theology in the first half of the 20th century,[50][72] but weakened Christian resistance to Hitler by stressing the perceived common ground uniting Nazism and Catholicism.
[50] Krieg identifies Adam's pessimistic evaluation of Western civilisation as the fatal flaw in his thought, which led him to seek accommodation with Nazism.
[73] Adam's theory of history, Krieg argues, was insufficiently complex and failed to consider the capacity of the church and tradition to adapt.
[74] Krieg suggests that Adam's life and work provides a lesson in the impossibility of "turn[ing] back the clock in order to restore the relationship that existed between the Church and the state in an earlier epoch.
[77] Writing in Commonweal in 2008, John Connelly argued that Adam's engagement with Nazism indicates "the dangers of speculation, of making judgments about the fulfillment of God's will in history.