Gustav Bergmann’s activity may be divided in three phases. The first one is mainly concerned with the philosophy of science, more or less in accordance with the teachings of the Vienna Circle. The second consists in the development of a rich ontology ¬– yet constrained by the principle of acquaintance –, aiming at establishing a realist view, both in the sense of realism1 (opposed to nominalism), and in that of realism2 (opposed to idealism). Such development goes along with a reflection on the nature and method of philosophy, culminating with one of the most perspicuous formulations of the ideal language method. The last phase, known mainly through posthumous writings, puts forth a revision of the previous ontology. In this account special attention has been paid to the second phase, for which Bergmann is mostly known, and its methodological aspects have been privileged in the exposition.