A friend of the painter Felice Casorati, he frequented art circles connected with the Accademia Albertina and was close to the Gruppo dei Sei (Group of Six) which reacted to the tendencies of the Novecento Italiano. He also acted as art consultant for the modern section of the collection belonging to the industrialist Riccardo Gualino. In 1926 he published Il gusto dei Primitivi, with an anti-academic and anti-classical bent.

From 1930, with his father he edited the new series of the magazine L’Arte. His refusal to sign the pledge of fidelity to the regime, imposed on university teachers, led him to emigrate first to France from 1932 to 1939 and then to the United States from 1939 to 1945. He continued his attention to modern art in works like Cézanne of 1936, Archivi dell’impressionismo of 1939, Pittori moderni of 1946, and problems of criticism, as in History of Art Criticism of 1936 (Italian translation 1945).

In 1945 he returned to Italy, where he held the chair of Art History at the University of Rome until 1955. He continued his work as an essayist with Pittura. Come si guarda un quadro. Da Giotto a Chagall of 1947 and as a critic alongside the Gruppo degli Otto (Group of Eight) (1952); he devoted his energies to the magazine Commentari, which he edited with Mario Salmi, and often acted as commissioner to the Venice Biennale.