He participated in the events of the university's Philosophical Society, as well as with private circles (especially Oskar Ewald, Otto Weininger and Othmar Spann).

The Kraft Circle, which he chaired between 1949 and 1952/3, was named after him, and it was during this period that he supervised the dissertation of Paul Feyerabend and Ingeborg Bachmann.

[4] Among the logical positivists, Kraft represents a unique standing point: he wrote about a non-sensualist empiricism with a hypothetical-deductive structure.

Before the First World War (and after it together with the Vienna Circle members) he dedicated most of his lectures and publications to promote scientific philosophy.

He also made important contributions to the establishment of ethics as science and wrote about the theory of geography and the philosophy of history.